For the American market I think you may do well staying away from some of the African calibers.( I know, blasphemy)
At any rate something like the .308 Marlin, .450 Marlin, 45/70 would probubly go over well. If you could go with rimless rounds (I know, blasphemy again) a .270, 30-06, .300 Win mag, .338 Win mag, .375 H&H, .416 Rem mag, and maybe a .458 Lott/ Win mag, all calibers the average guy could walk into most any hunting shop and buy ammo for without spending a full days pay for it.