> the ones I'm after are more angular
OK, I know the type.
Those are probably the old 5-lobe round knob, with added V-nick and a |_|-nick carved into the mold.
There is probably a 3/4-crate of them lost in a warehouse, unseen since Ike was in office.
In fact it looks JUST like example knobs from a human interface book published around 1960. Pilots and other harassed operators should NOT wonder which way a round knob is pointing, should NOT be likely to confuse radio with throttle... knobs should be distinctive and unique. That great idea lasted a week.
Try Nebraska Surplus. There are a couple other ham-radio junk shops in Middle America who may have knobs like that, though you might have to buy a whole radio module for the knobs.
A labor-intensive thought:
Nearly all such knobs are "cupcake mold", meaning all that you can see can slip out of a single mold like a cupcake. There would be another mold for the hidden side. Seems to me, though, with the explosion in resin plastic models, -somebody- could make a wax model, take a rubber mold, half-fill it with excess resin from larger projects, stick a cheap plain knob inside for an insert and set-screw (no back mold).
http://www.starshipmodeler.com/basics/jc_molds.htm
The hardest part may be "carving" a prototype. It can be wax or clay or wood, one-piece or stuck-together, whatever works; but it "must be perfect" because if one of the 5-lumps is off-size, or the chicken-beak is crooked, all your copies will have the same flaw and annoy your fingers.