What model is it? 12/14/24?
List some info...model and power requirement tag on the back or a photo.
There's one on Ebay mixer+PSU for like $50. It's in UK so shipping might be high.
Maybe they will sell you the PSU...
You would be better off buying that. Spare parts, manual etc etc.
You probably couldn't build a supply for less than that!
Do you have the manual, schematics?