The Calico might be too 'different' to have P90 base and anim.
It uses a hand restion on foregrip section, while P90 hand appears to look like it grips some kind of vert grip (as seen on Chang Feng)

AutoMag is being worked by other modder, and it's nearing completion

There's already IWI Tavor, although a different variant by >:3. And I have hunch that Overkill will add Tavor AR for H3H3 pack

TKB-076 mag is positioned way on the back, there's no anim or positioning could work with that kind of setup.

Someone already requested P99 here, but I think there's no good model to port it in.

I'm also looking to do CM901 AR some time ago, but the only game that features them is CoD MW3 and previous CoD before Advanced Warfare have imcomplete 3D model.

Barret M107 is also being worked by other modder, but idk if the modder is still working on it or not.

I'm actually waiting for a good source for HK MG5 to port that in as mod. So far the only good source for it is The Division and GR: Wildlands, and neither of those have proper asset extracting tool.

I'm considering G11 with P90 anim in the past, but it hit the same problem with Calico, limited base and anim of P90 wouldnt do it justice

FAD might be a good AR to port in, but the only AAA source is from CoD MW3, so same problem as CM901 above.

MP412 REX looks like every revolver, so it's very possible with any Payday 2 revolver base. Groceries have been doing some revolver, so perhaps he might take interest in it, if you ask him.