I've got lots of new production HMMWV's sitting all around me. I knows a few things about them.
Stomis is right, the 24 bolt HMMWV wheels that everyone is referring to are just regular steel wheels similar to the older 8 and 12 bolt versions but with way more bolts.
The newer HMMWV's all have Goodyear Wrangler MT/R's of the first vintage (2000-08 or so) flavor, not the current MT/R with the chevronish tread (2009-present or so). They are in a 37x12.5R16.5 size that isn't commercially available I don't think.
There's also a new BFG Baja in 37x12.5R16.5 floating around too. Think those were ordered for something else and then got throw into the general HMMWV population when the original purpose got cancelled.