If you have at least one of the original knobs, measure its OD, height, shaft size and shape. Then if you spot what looks like the correct type, PM the seller and ask him to measure the knobs and let you know their size and shaft size and shape. You might be able to find a match that way.
OR, measure the size of the control shaft, OD and length in front of the front trim panel, take note of the shape of the end of the shaft (splined for push-on knob or D-shape for push-on knob, or round for knob using a set screw). Then look at new knobs available from some suppliers such as Antique Electronic Supply, find a type that will fit and buy a set to replace all those unique knobs with new ones that will all look the same. The guitar manufacturers used a wide variety of knob styles and finishes over many years and AES has most of them covered. Alternatively you might find some current stereo equipment model that has knobs that would work and be able to order a set of them through a dealer.
Joe
