i think they are gone, their last EPA certification for the T4 was in 2016.
Here are 2020 Google Earth images of their 1650 E Riverview Dr. Ste 110 Phoenix, AZ 85034 location:
Per Import Genius their last shipment T4s from Asia was in February of 2007...
It appears you may be able to order on from the manufacturer; CHANGZHOU JOYNER RECREATIONAL VEHICLES CO.,LTD. if you are really in to self-abuse...
Joyner appears to be yet another example of a relatively successful ATV dealer who had a delusion of grandeur and launched a corporation to brand and market some attractively priced (for them) import ATV/UTV (probably located on Alibaba) but lacked sufficient resources ro pull it off long term. According to various corporate records (mostly D&B) I found the Changzhou Joyner Recreational Vehicle Co. has 50 to 100 employees with annual revenues of $1, 000,00o to $2,600,000--hardly a manufacturing giant.
Hisun USA has revenues of $9.25 M, not Yamaha or Kawasaki class certainly, but a lot more staying power. Chongqing Huansong Industries (Group) Co., Ltd. (Hisun's parent company has 1000+ employees, 9 subsidiaries and makes 70% of their parts (probably better than Ford or GM).
I'd look elsewhere...