Not exactly comparable but I used to use the Hirst Arts moulds for plaster of Paris:
http://www.hirstarts.com/molds/molds.html
Can’t find the UK webshop I used to use anymore. Has been a while…
Actually I did some more digging and it wasn’t plaster of Paris but something more akin to dental plaster. Used to buy it by the 5kg tub. Hmm. Wonder what I did with them?
