Hi Dan,
Welcome to cr0 Dan!

If you want to replicate British Indian Restaurant (BIR) curries, you're definitely gonna have to try and make your own! So you've come to the right place and made the first important step!

I suggest you consider trying Darth's curry base and Madras (here:
https://curry-recipes.co.uk/curry/index.php?topic=674.0). Many people have tried this and have had good results.
The same curry base can be used to make any of the other main dishes (including Chicken Tikka Masala) in the recipes section.
I agree that curries in WA (and elsewhere in Australia) are not the same as typical BIR curries (i.e. they can typically taste like they are straight "out of a jar"). I also know (from bitter experience) that you can get some absolutely bl**dy awful ones!

However, having said that, I've found very tasty and enjoyable curries in Perth (and in Melbourne). Have you tried "The Cove", on Canning Highway, or "The Turban" on Stock Road? Both supply a very enjoyable "eat as much as you like" buffet for about $25 (about 10 quid) a head. The Cove is an exceptional setting in a very attractive old colonial building. "The Madras", on Canning Highway, also produces a very palatable curry (though not "BIR-like"). I think it's "The Anarkali", in Northbridge, that does a very tasty and popular Thali for about $15 (about 6 quid) too.
Good luck with your curry cooking exploits! Just shout if you have any other questions!

Regards,