Where can I find a TH350 part?

[DRD57]

It's 3385 on this picture:
http://www.aceomatic.com/catalog/automatics/illustration.asp?t=7

It's the spring retainer ring for the piston all the way at the rear of the trans.

I tweaked this one beyond repair getting it out.

I thought it would be OK but when I air checked that piston when I put it  back in, the spring retainer pushed part way past the snap ring that holds it down.  It's gonna be a bear to get back out to fix.

[DRD57]

Thanks, I stopped at the local trans shop on the way home from work and they pulled one out of a parts TH350 that they had on the shelf. $20.