Not definitive, but definitely suggests that a pack of AN PBCM should be OK :

QuoteWhat Food Can I Send to Australia?

    Store bought foods in the manufacturer

Hi Livo
A quick fix for this elusive Bassar mix.

100g box of MDH Kitchen King, 40g of any chilli powder and 30g of Paprika.
put this together and add a drizzle of mustard oil
if you want it to clump up a bit, like they do in Mirpuri homes.

This will be a good substitute for the alchemist in you!
cheers ChewyTikka.

I have an unopened box of MDH Kitchen King in the cupboard, both Kashmiri and plain Red Chilli powder and Sweet Paprika powder so I'll give it a go. Thanks Chewy.

I didn't mind the concoction I made from the Eastern Fish Masala and it made a good curry. It did however have a very slight bitterness.  Could have been the Methi going into the Masala instead of added later in the cook.  I have 2 X 50g packets of the Mangal Kashmiri Masala (powder, not paste) on the way from a supplier in Melbourne.  The guy was really helpful and said I should be able to find it in Sydney as there are many Indian Grocers that would have it, just not online.  I don't intend on driving a 200 km round trip to a place I haven't found yet to buy a box of powder for $1.50. (less than a UK quid).

I made contact with a company that produces a well known brand of spices and mixes here in Oz. They have been around for a couple of decades so they are doing something right.  It turns out that the factory is fairly close to my home. The boss himself contacted me back and was very interested in Bassar.  I then sent him a copy of my research spreadsheet and he has told me he will investigate and get back to me.  In the mean time he gave me a formula that is not too dissimilar to what you have just advised Chewy.

1 tablespoon Curry Powder Medium Madras
2 teaspoons Chilli Powder Kashmiri
1 teaspoon Garam Masala
1 teaspoon fenugreek leaves (methi) powdered

I can answer that one  ;D ;D ;D

Although Bassar originally is a shortcut one pot spice mix.

The Midlands, Yorkshire, lancashire BIRs etc will probably use it as a normal Bengali mix powder.
Somewhere like Bradford, historically has a high concentration of migrants from Mirpur/Kashmir
and those that went into the restaurant trade will have brought their specific cuisine,
adapted for UK tastes of course.
If you go to the famous Mumtaz Restaurant, Bradford, for e.g.,you will get this Bassar flavour from their style of BIR cooking.

Although I like to experiment, its never been to my taste and not Bangladeshi BIR food
I was was brought up on and championed since I joined cR0.

cheers ChewyTikka

LC (or anybody else interested), the photo I posted above shows a 100g Box of "Eastern" brand "Fish Masala", with the following ingredients Kashmiri Chilly (sic). Coriander, Turmeric, Salt, Mustard. Fenugreek. Garlic, Dry Ginger. Eastern brand should be available in the UK but you could use other masala blend with the same or similar ingredient listing. Alternatively, I will provide the formula in grams of individual spices if you can't get a suitable base masala upon which to build.

There is also a piece of paper with my scribblings on it. This is where I extrapolated a proposed Hybrid blend after analysing 8 different commercial Basaar / Kashmiri products and online recipes and formula for Kashmiri Masalas.  What I noticed about the Fish Masala was that the listed ingredients were in common and in order with my Basaar research.  So it only remained to see what was missing and as these were minor quantity spices it shouldn't be too difficult to add them in and create a Basaar mix. What I found yesterday was that it worked and my home made Basaar concoction, developed from the Fish Masala, was the same as commercially sold Kashmiri masala products.

From recent posts LC, I understand you are not a fan of Garam Masala in Mixed Powder or Base Gravy, but I did note that 7 of the missing ingredients are basically GM.
Cumin, Bay Leaf, Cardamom, Cinnamon, Black Pepper, Cloves and Nutmeg. My spreadsheet calculations and best guess extrapolations suggested that between 3 and 4 teaspoons of GM added to the Fish Masala was 95 % of a Basaar done.

There were 4 or 5 other minor ingredients still missing.  Paprika, Roasted Cumin seed, Fennel and Amchur.  There is also some uncertainty about the listing of Fenugreek on the Eastern packet.  Is it Fenugreek seed or Kasoori Methi? To cover this I could add a small amount of each.  So to finish, I lightly roasted 1 tsp of Cumin seed and then ground it with 1/2 tsp of Fennel seed, 1/2 tsp of Fenugreek seed.  I added 2 tsp of Paprika, 1/2 tsp of Amchur and a good pinch of Methi leaf and added it to the Fish Masala and Garam Masala.

I didn't, but if you wanted to you could then rub the whole lot through with possibly up to about 20 mls of Mustard Oil.  This would make it clump and have the oiliness of commercial Basaar.  I figured you could add that in as you used it.

So my final formula for Homemade Kashmiri Masala / Basaar / Bassar is as follows.

1 X 100g box of Eastern Fish Masala (or similar)
1 TBSP standard Garam Masala (individual spices listed above)
2 tsp Sweet Paprika
1 tsp ground Kasoori Methi
1 tsp lightly roasted and ground Cumin seed
1/2 tsp ground Fennel seed
1/2 tsp ground Fenugreek seed
1/2 tsp Amchur powder

Roast Cumin Seeds.
Grind whole seeds and Methi leaf.
Combine and mix all ingredients.

Optional: Rub through with up to 20 mls of Mustard Oil.

Note:
Dagar Phool is not a known Basaar ingredient but the addition of it in the newly made commercial product was welcome.  This product also had extra Chilli heat by the addition of Hot Chilli Powder as well as Kashmiri Chilli.

Fish masala substitute: Makes 100g.
50 g Kashmiri Chilli
20 g Coriander
10 g Turmeric
5 g Salt
5 g Mustard Powder
5 g Garlic Powder
5 g Ginger Powder