If there's a set screw on what's left that held the mast in place you could easily find the mast at most auto parts stores. Or possibly buy a new antenna that has a similar swivel joint & just use that portion.
Danny & Linda
Sold '13 Thor Redwood 36 FB
Traded '13 GMC Denali DRW D/A
Currently RV & truckless
Try unscrewing the short part that is sticking out of the pivoting base. On our 2015 Windsport 27K the antenna was all cracked up and falling a part. I was able to unscrew the mast and was able to find a generic replacement at the local NAPA store. The new antenna came with multiple threaded connectors that enabled me to attach the new mast to the existing base. There was no need to change the base or wiring. When you get that threaded piece out I would take it to the parts store, it may help insure you get the right adapters. My replacement has been in operation for about 18 months and still working fine. Good luck.