Does anyone know of a place where you can get cheap post mount disc brakes for 160mm rotas without the rotas? I just need to change the disc brake mechanism, not the rota!!!

Mechanical or hydraulic ?

Is there a brand or model that you are specifically interested in ?

What do you call cheap ?

No brand or model, mecahnical and cheap is anything up to about £20. Possibly a little more if necessary.

ebay.

I bet you could find a BB7 for cheap I got a pair for $20 on my local bike forum.

BB7 on ebay

and "rotor"