Distributor advance springs

Hey guys. I have an issue with my 74 Dart Sport, 77 Slant Six, where it runs great at idle or low RPMs but at high RPMs it develops a spark knock. To mitigate this issue, I’ve plugged the vacuum advance hose and slightly retarded the distributor. This keeps the knock to a minimum and limits it basically to only high RPMs like 65-70 mph (with 3-speed) before I hear the knocking start. My dad has been working on these cars forever and he says he thinks my distributors centrifugal advance weights are stuck in an outward position, or the return springs are broken. So my question to you guys is, is there somewhere I can go to buy that hardware? A new slant six distributor is prohibitively expensive at the moment, so I’d like to simply rebuild mine if I can find the hardware somewhere. Thanks in advance