I ordered a couple of soap stamps from a vendor on Etsy. They were dirt cheap and traveled here all the way from China in no time at all.
Learning to use them has been an adventure. You pound them in with a mallet. The soap has to be soft but not too soft. That should say Soap Handmade but as you can see, I don't quite have it down yet. This is my baby buttermilk soap with carrot puree that is almost all olive oil so it's still a bit on the soft side.
The little bird worked out a bit better but I can still see the edges of the stamp. Not good. All the tutorials say this is a matter of trial and error. I don't know about the trial but I sure have the error part down.