It won't be as cheap as the bottom of the barrel plated and/or 'silver' plastic; but (as is...oddly common...in situations where art overlaps with other areas that use the same parts) you might have better luck purchasing from somebody who supplies industrial knobs to industry.
Good old McMaster-Carr is Not Exactly the bargain choice; but they do have a lovely selection, including knurled knobs.
MSC Industrial Supply also has some reasonably promising candidates in "Handwheels, Levers, Handles & Knobs". (Conveniently, many sorts of machine tools require proper knobs for adjustment, so there is already a market for good, solid, industrial, fiddly bits)
You could also look for suppliers of 'panel mount' potentiometer and rotary encoder knobs; but(while sometimes finely crafted) those tend to be a bit less 'industrial' and a bit more radio age/Cold War chic. Not necessarily a bad thing; but answers to a different question. Electronic Goldmine is, alas, sold out of their 25-knob assortments; but still has sets of 7 and individual Raytheon knobs. The assortments are, shockingly, a bit of a mixed bag(some totally undistinguished, some definitely rock the 'control panel for the tube-based doomsday computer from an alternate universe where transistors were never invented and the Cold War never ended' vibe). The Raytheon units are more uniform, and nice knobs; but also more 'Colossus: The Forbin Project' than 'Industrial'. Not that I, um, don't own several now, for reasons that are totally defensible.