Mike, I can only speak for the 1/48 scale and there the best P-40 kit you can get comes from Hasegawa. I have built a few of them already and they go together without bigger problems. Hasegawa has the E- and N-version in their program. Further there is still the old AMT-Ertl kit (M-version) available, now in Italeri boxing. It is a bit cheaper than Hase but it gives you also some more hassle ....
If you're lucky you might even get the Mauve kit. Hobbyboss also brought out the P-40 M in their Easy Assembly Series. But I can't tell you about it, because I still don't own that kit. Remember, all these kits are in 1/48.
And speaking of unusual P-40 markings, don't forget the brave
Finnish Air Force. They also "got" one P-40 M, sponsored by a friendly russian pilot ....
Happy modelling
Torsten