You could order from DSA but you will likely have to wait months for it to arrive. I'd call ahead and ask about the potential wait time (and then double what they tell you ). Same goes for ordering a DSA from a third party. Obviously if you find one in a local shop you won't have to worry about waiting, and you'll be able to handle it before buying.

FWIW, you can get great deals on an FAL by buying a used one, with not much difference in quality. Also you won't have to deal with the wait obviously. I'd say check here, cologunmarket.com, and the FAL Files forums.

As for ammo, in general I'd say it's perfectly fine to use military surplus .308 in an FAL, new or used. That's all I use in my FALs. There are some exceptions, though. Do you have anything in particular in mind? Post the country of origin, year of production, and headstamp if possible.