Here's a link to my design service info:
http://albanach.org/design.htm

You can also commission the STA to design the tartan for you. Also, STA members get use of their consult service (so you can confirm with them that a tartan you designed is going to be registerable before you go off and have a bolt woven).

And getting cloth custom woven doesn't have to be bank-breaking. We can get a small run of 4 yards done:
http://giftshop.scottishtartans.org/custom.htm

And it doesn't necessarily have to be commercially produced. If you know a hand weaver, you can have a small sample woven up for registration. They only need a sample large enough to show a full sett repeat to record it.

M