I concur that Gamebore is the best option in Canada for 65mm compatible shells. That said one could probably get away with using 2 3/4 skeet loads without much problem. Under no circumstances would I suggest heavy field loads.
Another option is to go the reloading route and simply cutting down 2 3/4 hulls to 2 1/2 and either roll crimping or modifying a MEC Press to crimp them. I find the roll crimp route relatively painless and I get a real kick out of using the roll crimp shells.
Lastly SKEETTX I too have a 28 gauge marked with 3in chambers, though my is a plain jane Riunite Armi - E. Salvinelli (not an A&S) O/U from the early 60's. I believe it may still be possible to find 3in 28ga hulls in europe, though I not sure one should.
