Good News!!
Old Holland is selling their w/c Indian yellow series, Gr/s, Br/s and Org/s. This is a first and without a doubt the best transparent yellows since they already sell the best Indian yellows in oil paint. Indian yellow is finally getting the attention it deserves. Forget all other brands, this will be the one to compare to my home-made paint.

I bought them from Art Supply Warehouse, 1-800-995-6778.
I think they were $12.50 each. I can't wait until they arrive.

That was in 2005, today is 2-6-13 and I have a new best water color, ink-jet ink, and acrylic transparent yellow. It's called Tartrazine Azo yellow, PY100. The market doesn't know about it yet, it's not in a tubed color or ink cartridge yet. But I found it. It's just like the original indian yellow in every respect, including permanence. I got the dry pigment direct from the manufacture, Spectrum Color in NJ. I've made 3 pages on this new Indian yellow.
http://www.realcolorwheel.com/rcwplotter.htm  The ink.
http://www.realcolorwheel.com/indianyellowtobrownTartrazine.htm  The pigment.
http://www.realcolorwheel.com/indianyellowtobrownPY153.htm   The acrylic paint.