Adding PCV port to carb

Trying to add pcv to carb, It's a Barry Grant Silver Claw. It has a 3/8" hole drilled in throttle plate, with a metal plug pressed in. removed the plug. but the hole is too big for a 1/8" NPT, and it looks like 1/4" NPT will leave a very thin side wall. So where do I find a press in 3/8" fitting?

Thanks