Eve, if you have already tried the usual suspects, as far as espresso supply shops, like Visions in Seattle, your next step wouold probably be to shop in some art supply stores for an unusual single punch tool.
Being able to search effectively is a gift ;-] (aka - No problem)
epsressoparts.com has lots of punches and stamps. in some really cool shapes / designs.
go to espressoparts.com for everything.
jon <- not affiliated with EP just love a great set of people and great products.