Regarding the Silicone:
This supplier is very good, good communications and service:
http://www.tomps.com/
The products I've used are:
Polyurethane Fast Cast Resin 2kg kit RTV Silicone Mould Making Rubber 1kg
I used the fast (blue) catalyst with the RTV Silicone and it cured pretty quickly but with a useful working potlife too. The resulting rubber mould was excellent. The Polyurethane Resin is easy to mix as it's 1:1 by weight and makes for a very thin liquid resin which is easy to cast and makes a very durable tough moulding.
Definately worth trying those products, the RTV is flexible enough to allow a one part mould provided there's no really deep undercuts and the RTV Silicone doesn't need a mould release using the polyurethane fast cast.
If you need any help Tony at TOMPS.com has a datasheet and some info sheets on the products too.
Anyhow hope that helps and Welcome to the forums!