A lot of 6-8" fish. 9-10" are harder to find. 11" and up are really hard to find, with most being show type fish because the larger ones always seem to have a look unique.
I would have to agree that they are slow growers. O have never seen one over 12" but I am kicking myself for not buying a 10" male I saw in a LFS. I passed because of split fins.
GT's are awesome when they get nice size nuchal humps.