Sure!
SPAM is an acronym for Shoulder (S), Pork (P) and Ham (AM).
It is small 'trim' that is chunked, seasoned, cooked and mixed with a binder. It is then forced into the can and cooked and sterilized at the same time. When cooled makes the pate-like substance we all know and (mostly) love!
To make your own, cube or dice any of the above (S,P, or AM) that you have or care to deal with. Boil it lightly in order to get rid of as much fat as possible and season to your liking.
I would cheat at this point and use commercially available gelatin as a binder since I don't have access to the food science that the SPAM folks do.
I would then pack it in carefully cleaned cans, put the cut-off lid on and place a weight on the lid while it cooled in the fridge.
Note that this is not "canned" as in preserved (use mason jars and a sterilizer for that), but will keep for quite a while if refrigerated.
To use, cut the bottom off the can and push it out, slicing off happy slabs to make sandwiches or fry up with your morning eggs!
Best wishes!