Re: Seymour Duncan 300x2 Bass amp, knobs needed...
Welcome to the forum.
Good luck. It's great you're trying to restore it to original condition, but I doubt you'll find much. Kind of like me looking for gray teardrop-shaped knobs for old Univoxes - when I built my clone, I just had to settle for black.
Those knobs are similar to, but probably larger than the "Davies" (model 1510 pointer) knobs that are popular with boutique and DIY pedal builders, most notably Fulltone. If it were mine, I'd move the original knobs around to fill up a section, then replace the remainder with black Davies knobs. For example, if I had eight originals, I'd put them on the volume and EQ pots, then put Davies on the lower row (crossover and tone controls). If you have fewer, use Davies on the EQ and originals elsewhere.
If it will help, I'd be happy to send you enough real-deal Fulltone knobs to cover your empty pot shafts. I have a bunch, and they are much better-made than the Taiwanese clones commonly available. Lemme know... Here's a couple on my modded DS-1:
P.S. How 'bout a pic of the whole amp? I don't recall ever seeing one before.