Talk to CafePress directly-- I don't have any more pull with them than you do.
Printing on dark fabric is a trickier process than printing on light colors, so they have a more limited range available. There's a long-sleeved dark tee that you might consider.
Also, I don't know if folks noticed, but the dark tees usually have more than one color available, not just black, as do many of the light items. You see the color options after selecting the item. Example of the shirt I posted earlier with a different color selected:
And here's one of the other choices on the dark tee (not the women's T):
