Hi Matt
Standalone connectors like you want are very difficult to come by. Here are some ideas.
Steve KC4WN (eBay ID
kb4dmf). Steve posted last April (on the ARC-5 reflector) that he acquired all of Bill Perry's ARC-5 connectors.
Steve's email is
swkb4dmf@windstream.net, or search for "SCR-274N" on ebay and you'll see connectors sold by "seller kb4dmf". Quite a few of us have purchased from him and he's a reliable seller.
Send a post to the ARC-5 reflector. Most people on that reflector are also on this one, but you never know.
Steve may be able to help with the rack connectors, but the connectors for the back of the transmitter and receiver may be a different story.
When the rear connectors were removed "back in the day" and replaced with octal jacks they were trashed as nobody back then figured anyone would want them in 2023 AD. With hamfest season coming up, I suggest you look for ratted out junker units; some may still have the original rear jacks.
73 Mark K3MSB