Hi Tim,
In addition to the AML decals Mike posted , there are quite a few goodies out there for the 1/72 P40B.
I did a quick ebay search using '1/72 P40b' and came up with 145 listings including kits and accessories.
There are two different sets of canopy masks listed by Model Maker and Montex.
A couple of cockpit / detail kits by AML & CMK.
CMK also makes a set of undercarriage doors, exhausts and an engine set.
2 sets of PE by Eduard.
Wheels by SBS - I think True Details also makes a set.
Quickboost makes several sets for the P40B including 2 sets of exhaust, Undercarriage doors, and a prop set - plus more.
Aires makes a set of wheel wells and also a set of wheels.
Theres quite a bit out there.
Hope this helps.
Adrian