Cementex Latex Corp.
They provide a wide variety of materials for making rubber molds. Compound natural latex, urethanes, polysulfides and silicones. They have also produced an extensive video on Making Molds With Natural Latex and an equally extensive video on Making Back Up Molds for natural latex.
This Plaster Master site is a one stop source for a wide variety of molds. Their selection includes molds for ornamental plaster and concrete. They also have a link for used molds.
(I like used molds)
Deep Flex Plastic Molds by Yaley
They carry molds for many different applications, including plaster, resin, and concrete casting, as well as candy molds, candle molds and new soap molds. They have an extensive line of accessories, tools and finishing products includes everything from beginning to completion for any casting project. They also manufacture custom plastic molds.
They offer a quality selection of molds, Concrete, cement and plaster casting molds
Heavy duty molds for the concrete or plaster casting industry. AllMolds.com offers a great selection of unique molds. Great for the home hobbyist or professional