In the US , you will find 12g , 30-30 and 30/06 are very common , almost any backwoods store will have these .
Once you go over seas , look for the 30/06 , 303 British and the 8mm Mauser to be quite common ( Africa ) and as for Europe the 7 x 57 & 8 x 57 Mauser's should be no problem .

stimpy