Anything up to 3"
Google a company called Polywad. I have bought shells from them and was satisfied with their product.
You will have to do internet searches to find out. I do not know what "cheap" means to you.
Gun shops, gun stores, sporting goods stores, ammunition retailers, internet
If the barrel says"2 3/4 inch shells", don't shoot 3 inch magnums. You might get away with it for several hundred shells, or you may crack the stock or forearm with the next shell you fire. If you want a magnum, go buy one, and save the Auto 5 for pheasants quail, and rabbits.
To get shells you must buy them, or win them in contests!
A Benelli Super Black Hawk. It shoots 2 3/4, 3, and 3.5 inch 12 guage shells and is excellent for everything you mention with possibly the exception of trap which I have never shot. I have, however, shot sporting clays with my Super Black Hawk. (not an answer) Well... i kinda posted this in hopes of an imidiate response... which didnt happen haha i ended up getting a berreta 26in barrel and shoots a 3
you dont go to the sea shore to buy egg shells
where can you buy shells for 44 shot steven
You might try eBay or post in the Want to Buy sections of some of the firearms related websites.
The Beach or souvenir shops. I find they have good fake shells :)
beach
Try gun shops, gun shows, estate sales, garage sales, pawn shops, for sale ads, want ads.