does any one make a single point threading tool to turn a 1/4-20 thread on an internal surface? it would be ideal if it was a carbide insert tool.

how about this, but it's not an insert based tool:
http://www.littlemachineshop.com/products/product_view.php?ProductID=1895&category=8

is tapping the thread not an option?

tapping the part would be an option, but i have to make 500 of these so i'd like to automate it as much as possible. i'm running mach 3 on my lathe and i don't know if it has a G code to run a tap.

wear on a single point will be hard to control, you would be better off tapping, either with a tapping head or gain control of the spindle. At 500 pcs you will be changing taps or tools either way.

chris