TASCAM M-1516 M-2516 M-2524 M-3500 M-3700 knobs in various colours S656+
These type knobs have a habit of turning Brown and thats not always because of smoke but because Bromides are leaching out of the plastic (at least thats what the book says). price each but I can do a deal for 10 or 20 in a mix much better.