Little late to the party peter, this was from last year.
If you need a new heated bed there are three options:
a) Makerbot will sell you one (might have to call them if you can't find it on the web store)
b) You can get one etched - there were even designs for an open source version at one point
c) You can make your own. I did for my cupcake. Makergear sells most of the pieces
http://www.makergear.com/products/plastruder-replacement-parts - Nichrome wire is the fundamental heating element. My heated bed is basically a length of Nichrome wire epoxied to the steel from an old computer case, and all three of the insulation products they offer sandwiched underneath. I used their hot end epoxy... which is no longer available as they don't use it in assembly...