I will be in or about a jurisdiction in Ohio that doesn't allow 'assault rifles'.

I want an AR type rifle for varmint type shooting. I see Bushmaster has a Carbon-15 carbine with fixed/sealed mag well, requiring top loading a max of 10 rounds.

Given my purpose, Varmint hunting/paper punching, I can deal with a fixed mag AR (whilst keeping my 'assault' ARs in a different jurisdiction.)

Can I get this Bushmaster Carbon lower anywhere to build a 20" - 24" varminter on?

Does anyone else sell a fixed mag lower?

Quoted: Does anyone else sell a fixed mag lower?

Yes there is the 'FAB-10' lower (they are in the industry section).  They sell an aluminum lower with a fiexed 10 round magazeins.

Vulcan also sells such a lower, but given their history I wouldn't even consider it.

I wouldn't recommend the Carbon line under any circumstances.  If you must have an auto loader, look into that Fab-10 thingy.