Just FWIW and FYI I found a full range of polystyrene caps in tolerances of 0.25%, 1%, 2.5% and 5% here:
https://www.surplussales.com/Capacitors/Poly-Unelco.html
For smaller values and low voltage they can be fairly small.
Btw, in the end I chose the very hi-$$ BB OPA627 di-FET b/c of too many good online comments re its sound and I tended to agree after trying many including the 1656. The 627 just sounds clean. The pictures linked to by Marcel in post #15 is my 1st pass and I made the mistake of buying exact 1% values but high voltage so those were rather large and my layout sprawled. #2 version uses 1/2 low-voltage combo PS + 1/2 Wima MKP in combo, hand selected.
https://www.surplussales.com/Capacitors/Poly-Unelco.html
For smaller values and low voltage they can be fairly small.
Btw, in the end I chose the very hi-$$ BB OPA627 di-FET b/c of too many good online comments re its sound and I tended to agree after trying many including the 1656. The 627 just sounds clean. The pictures linked to by Marcel in post #15 is my 1st pass and I made the mistake of buying exact 1% values but high voltage so those were rather large and my layout sprawled. #2 version uses 1/2 low-voltage combo PS + 1/2 Wima MKP in combo, hand selected.