Other than HTA, there are other vintage racing organizations that are recognized by SCCA and which may hosts races within SCCA programs...
The following organizations’ licenses are currently approved by SCCA for competition in Vintage/Historic
events:
1. Classic Sports Racing Group (CSRG)
2. Historic Sportscar Racing (HSR)
3. Society of Vintage Racing Enthusiasts (SOVREN)
4. Sportscar Vintage Racing Association (SVRA)
5. Vintage Auto Racing Association (VARA)
6. Vintage Motorsports Council (VMC) and VMC member organizations
7. Vintage Driver’s Club of America (VDCA)
Maybe HTA is more a west coast organization? I saw vintage TA type racing at Road Atlanta a few years ago and the sponsoring vintage organization wasn't HTA, but I don't recall which one it was...? Maybe someone more versed in these organizations / events can give us a tutorial?