Awesome...this thread started 5-1/2 years ago!
I'm sure it's been said, but an SKS.
More non-shell ejecting multi-BB shooting pump shotguns.
These might already exist, but Ithaca Model 37.
Winchester M1897 and Model 12 trench guns.
Stoner 63.
Or Marushin making their M500 in 6mm again.
Actually, now that I look at my list it looks like I'm itching to get some kind of Vietnam loadout.