You could go with vintage Play Doh molds from Ebay. (I literally dug up an old Yoda mold of mine in the yard years back). Looks like they still make some sorts of those, too. Also there are Star Wars cookie cutters.
Thanks for the shout-out! Although I’m familiar with making one’s own molds and then casting items using polyurethane resin, I’m not aware of any pre-made molds for use with clay. Darren_Garrison’s suggestion seems like the way to go. Something like this, perhaps: Vintage 1977 Star Wars Play Doh Action Set! | eBay
I’d look for things like jell-o molds and even ice cube trays too. Fortunately George Lucas had no shame or restraint whatsoever when it came to merchandising, so such things should be fairly easy to find.