If a US citizen wants to bring a shotgun to Argentina for bird hunting, what are the requirements?

Are 28 gauge shot shells readily available?

You may bring 2 shotguns, I understand. Look for the web page of the R.E.N.A.R. (Registro Nacional de Armas), there is an English version. There is a fee of $100 for each firearm and you must declare them at the nearest Argentine consulate. Ask your outfitter, of course. The 28 gauge shells are readily available in most cities but you must have a special license for buying, thus the outfitter-guide should provide the shells.
Good hunting!

There isnt any problem bringing any type of gun to Argentina including handguns ,the goverment is strongly antigun ,but never touched this ,because they need the us dolars for their populism politics .Juan

I agree with Juan. Call your closest Argentine consulate and have them send you the forms for the import permit. That speeds things up once arriving in Argentina. The last time I went with my guns the charge was $75.00 each. The
consulate charge was $40.00 total. They would also know the current entry fee.