Re: NPO Capacitor source
I was looking for something similar a couple of weeks ago and I bought these
55 Values 1100PCS 0603 (1pF~1µF) SMD capacitor Assortment kit #U1
from umisky*2014 I paid £13.20, which seems expensive, but it is only about 1p per cap.
This is a general selection; up to 820 pF is NPO/COG. There is a table with the values and types of cap.
From memory, I searched for something like NPO capacitor assortment Other words like kit and range may also be useful. I know, you can waste a lot of time in these searches.
Separately I bought a lot of 1 nF NPO. Above 1 nF, NPO caps become rare and expensive. Just keep your eye out for the bargains which often come up.