I am not sure of anyone who specializes in "Vintage" hemi parts. There are places that sell new hemi parts. I do see pre 426 parts in our want ads all the time. You have to look on a regular basis. HAMB market place.
I may have been confused. You are correct PAW only sells hemi bits now. I read "Vintage" and my brain said Vintage parts. Last I checked PAW was selling parts for old hemis really reasonable. @Speed Gems this is damned good info.
PAW: http://www.pawinc.com/ https://www.ebay.com/usr/vintagespeedequipment?_trksid=p2047675.m3561.l2559
Here's a link I found, post #46 has a PDF to their catalog. https://www.jalopyjournal.com/forum/threads/what-ever-happened-to-paw.1184966/
I have bought quite a few pistons from Ross but they are always backed up at least 3 months if not more. I think it may be easoier, cheaper, quicker to find used parts. I waited a year for my SBC pistons.
Try Brendan Murry at race car parts.com, he deals with nostalgia racers as well as new parts suppliers. I would think Hot Heads would stock pistons and rings for different uses. Did you get to make a few p***es at the Mooneyes deal?
I had my '55 331's forged pistons made by RaceTec. Four years ago they had a three week backlog, no idea nowadays. http://racetecpistons.com/