They don't make pre-upholstered re-pop door panels. However, the doors are the same shape as '55-56 chevy so you can buy basic bare panels and have them upholstered to match relatively easy.

1955-1956 pontiac share a lot of the same parts as 1955-1956 chevy. Try the chevy places first before paying pontiac prices. Most pontiac parts suppliers buy chevy parts and mark them up 10-20% if they can.

Knobs are not currently being remanufactured as far as I know.

Parts sources are: California Pontiac Restoration "CPR" www.pontiacparts.net
Ames Performance www.amesperf.com
Kanter www.kanter.com

good luck.