Devere 504 with jammed filter knobs

Well they aren't exactly jammed, they spin freely and the filters don't engage. I've had a look and can't see why. They operate with cables. It's an old Dichromat head.

Does anyone know of a shop that repairs these beauties?

Also, one or 2 of the filters are smashed. Any idea where I can get replacement glass filters?

Thanks,
Tom.