They're not original to that bike, so I wouldn't put too much effort into attempting to locate a match or a replacement part for that one.
Rupp used a chrome internal coil shock on their Continentals.
Sometimes, you can get lucky and find a nice set on a 1968 C350/C500, or a 1969 Sprint/Digger.
But if you're just looking for something that'll work for what you need, OldMiniBikes has adjustable shocks that at least look similar to the original Sebac shocks that Rupp used on other models:
https://www.OldMiniBikes.com/shock-3-8-hole-id.html