Cast your own replacement control knobs..?

[Whirled One]

Ever aquired an old TV or radio with one or two small knobs missing?
Sure, we all have!
...But finding a replacement that matches the existing knobs can be difficult...

Nowadays, there's a variety of easy-to-use flexible molding products on the market (some of which are readily available at various craft stores) and it occurs to me that this sort of thing might be well-suited for making molds of radio/TV control knobs. Has anyone out there ever tried casting knobs this way..? If so, what did you use for making the mold and for casting the knobs? Is casting resin strong enough to handle the torsion/twisting force on a control knob, or do you need to reinforce it with metal tubing or something?

I realize there are some additional complications to doing something like this, but thought I'd throw this out to see if anyone else has tried it before.