What size are you thinking? Andrews in Oz has reasonable quality Chinese optics in the 6-12" range (
http://www.andrewscom.com.au/site-section-10.htm). They also have the cheaper focusers,finders eyepieces etc.
Astrosystems in the US sells heaps of ATM stuff.
http://www.astrosystems.biz/
Protostar sells secondaries, spiders and holders.
http://www.fpi-protostar.com/
You can also buy a secondhand dob and use the optics for your own project. They come up regularly here on the buy/sell section. Often sold by people who find moving the commercial solid tube or split tube designs a pain.
If you want larger or the very best optics then you need to talk to Mark Suching here in Oz (
http://users.tpg.com.au/masuch/dso/) or order from the US.
PMing is OK but using the forum will give you a wider range of answers and allow others to learn from your project too!