MTB Chain v. BMX Chain

I'm new to the forum but it looks a mine of useful information so I'll give you a problem that has been bugging me for a while.

I'm in the process of renovating my daughter's old bike for my son. It got banished to the shed and raided for parts because the chainring got bent and I could never get it straight again.

The bike in question is a kid's mountain bike built on a BMX-type frame with a BMX-type one piece crank. However, because it has gears, it has a 3/32" chain not the usual BMX-type 1/8" chain. At the moment it has a GT BMX chain ring that I modified with a grinder so that the chain didn't get stuck on it but what I really need is a BMX-type chainring with about 40 teeth to take a 3/32" chain.

Any ideas where I can get one?

Thanks.

Not necessarily in this order:

Danscomp.com
LBS
eBay

if it has a deraileure there is a chance of the bmx chain not fitting through the deraileure. even if it does fit there is a big chance of the chain getting caught when your son goes to change gears and ripping the deraileure off.