HP 3312A pushbutton covers and knob

[belzrebuth]

Hi all,
I've just received a HP3312A from eBay that has some signs of abuse namely
two of the range push switches' covers are broken off and one vernier top knob is missing.
The vernier pot itself is okay and the switches work fine too so it's purely cosmetic but I'd like to get this thing in better shape.
Does anyone know where I could find these pushswitch covers or the knob?
Compatible are fine so no need for HP spares as long as they fit.