Will a...

[novice]

BMX chain fit through a rear derailluer. I want to know this because on my singlespeed I use an old XT derailluer to tension the chain and I should replace the chain. Was thinking of using a BMX chain for there strength, and the cool gold colour you can get those in.

[bomberz1qr20]

Short answer:
....Hell no

I assume by BMX chain you mean a 1" x 1/8" chain. Those are too wide, and will destroy the pulleys and cage in a 8 speed and especially 9 speed deraileur.
3/32" chains, and the like, are plenty strong for most riders, and are almost as cheap in some cases.
I think KMC even makes a gold one

[bomberz1qr20]

See this:

http://home.earthlink.net/~kmcchain/english/x21chain_intro.html

[novice]

where can i get one?

[DaveW]

Ask at your local bike shop if they dont have it they can order it in for you :)