My wife discovered you can order Legos individually directly from Lego. It costs a little more but you can customize your own package and get just the blocks you want.
Lego individual blocks
You just go in and select the bricks you want, how many of each etc. You can even select the color (my brilliant wife even color coded mine so I know the size brick by color, 2x2 = yellow, 2x4 = green, 2x6 = blue, 2x8 = red).
For those of you wondering why is this guy talking about Legos in the resin forum, Legos make great forms for molds.
BTW the link is good but it looks scary with that warning=false bit on the end, if you don't trust it you can go to this link and select indiviual blocks
Edited by Aaronw, 02 December 2007 - 07:04 AM.