You are making a smart choice of cartridges for general hunting by picking a 280 Rem. The AI version will use a bit more powder, shoot a tiny bit faster, and wear out the barrel a bit sooner - but it really will not do anything that the standard 280 can not do. I have used a standard 280 on critters from pronghorn to elk in North America, and from duiker to eland in Africa.
There are a good many rifles chambered in 280 if you look hard enough. Try looking at gunbroker.com or budsgunshop.com if you can not find one locally. An alternative would be to buy almost any long action rifle that shares the same bolt face (30-06, 270. 25-06, etc.) and have it rebarrelled to 280. Trying to change a sporter weight 280 AI barrel into a standard 280 will not work.
Is there a specific rifle manufacturer and model that you have in mind?