Hi!
I suggest that you spend some more time reading and learning first. Read the Wiki [
www.reprap.org] first, in detail. Download the RepRap host software, and install it and the libraries it needs. Get used to playing with it. Seriously consider patiently waiting for RepRap 1.0 to be announced (months from now, if all goes well).
To (partially) answer your question: You can buy most of the electronics parts from Mouser or similar large online electronics places. You can buy some of the hardware from McMaster and smallparts.com. See [
bom.reprap.org] . Acquiring the RP-able parts for a RepRap Darwin is currently either very very expensive (US$2000 or more) or needs a friend with a StrataSys or similar who can create them for you at cost.
If that confuses you, you are probably not yet ready to start building a RepRap. It's not a simple project. It's not even released yet. It doesn't fully work yet. Don't spend any money on parts unless you are *sure* you know what you are getting into here :-)
Jonathan
