OK... some more:
Places that will make stuff for you:
eMachineShop -
http://www.emachineshop.com/
LaserMade -
http://www.lasermade.com.au/
Precise Parts -
http://www.preciseparts.com/ppmain/index.html <- these people make special one-off parts to order, the website will give an estimate.
DiscMounts
http://www.discmounts.com <- the ultimate Alt-Az mount, with encoders for Argo Navis
Alpine Astro
http://www.alpineastro.com <- heavy duty equatorial mounts
Parallax Instruments -
http://www.parallaxinstruments.com/ring.htm <- great source for tube rings, will make special sizes
Bray Imaging
http://www.brayimaging.co.uk/Astro/telescopes.html <- Tablet mounts, GIRO mounts, Russian Maksutovs
Adorama -
http://www.adorama.com/ <- eyepieces, Vixen bits
BHPHoto -
http://www.bhphotovideo.com/ <- eyepieces, Vixen bits
Astro Physics -
http://www.astro-physics.com/ <- mounts, high end refractors
Kokusai Khoki -
http://www.kkohki.com/ <- Japanese eyepieces
SDM Telescopes -
http://www.sdmtelescopes.com.au/ <- Large Dobsonians, Stellar Vue dealer
Stellar Vue -
http://www.stellarvue.com/ <- Triplet APO's, alt-az mounts with encoders for Argo Navis
Another list of suppliers:
http://www.amateurtelescopemaker.com/cp.htm
The Cloudy Nights site has a useful (long) list of sponsors and Sky & Telescope has a list of advertisers, both worth trawling if you are looking for something. And don't dismiss BHPhoto or Adorama, you'd be amazed what turns up there.