look for instamold or some kit at wal mart or hobby lobby for making impressions of kids hands. then just double up the molding material (alginate mostly, or some kinda paper mache) and make your own hand.
the casting agent is plaster, so if you wanted something like hot melt vinyl or silicone... no idea for that.
plaster though, is normally included in the KIT to make the kids hands/feet impressions. they also sell spare plaster to make more than one casting as a "Refill plaster" kit.
instamold is pretty cool though. ive used it even with castingcraft resin and it holds up pretty well.
chris