If you have a reason to cut out un-mounted rubber stamps, you simply must acquire a pair of Kai Scissors. Oh my goodness! They cut rubber like it was butter. Trying to cut rubber with regular scissors is about like using a hack saw on your hair. The results are just not good.
Don’t cut rubber without them.
Incidentally, none of the stores in this area carry Kai and I was surprised at this. Even the ones that carry un-mounted rubber sheets regularly didn’t have them. (They sell for about $20. If you need a source, let me know.)