Try a spice mix that contains some paprika (a la Bruce Edwards'), and a three or four tablespoons of pasatta or blended tinned plum tomatos, the latter helps with the sour taste, without being too obvious like lemon/lime/vinigar or tamarind.
Or as suggested above, use Deggi Mirch, if you can't find that, some extra hot chillie powder used WITH some paprika works equally well in my opinion, I've tried both.
Or as suggested above, use Deggi Mirch, if you can't find that, some extra hot chillie powder used WITH some paprika works equally well in my opinion, I've tried both.