I don't know how you people eat, but one fresh ham isn't going very far at any reception I've been to, no matter how modest.
Peoria is where I get my whole piggies. Smallest you are going to find is probably in the 100-120 lb. range at around a buck a pound. Since a common estimate is 1.5 lbs. per guest, a 100 pounder is in the ballpark. What's the worst that's going to happen if you end up with extras? You'll have no problem giving some away, and it's cheap.
Of course a couple of hams isn't the "same thing." You can't put a funny hat and sunglasses on a ham. And there are no ribs, ears, snoot or tail on a ham. Or a loin.
PS, ask a manager. The floor guys don't enjoy walking across the street with a large animal and might fudge about whether you as a retail customer can have a whole pig.
And why would it be cheaper? Peoria is in the business of breaking down whole hogs. Other than the guy who has to fetch the pig, they are saving labor by selling you a whole one.
It is trickier and more work.