It is still being sold solo:

https://www.amazon.com/Goovis-GOOVIS-Wireless-Cast/dp/B08ZCMGGD9/ref=sr_1_4?keywords=rokid+wireless+adapter&qid=1679580412&sprefix=rokid+wireless%2Caps%2C285&sr=8-4&ufe=app_do%3Aamzn1.fos.f5122f16-c3e8-4386-bf32-63e904010ad0

It's a goovis product that Rokid bundled

If you're patient, the Rokid Max is coming out soon, which is probably much better than air.

Here's the wireless adapter link: https://www.amazon.com/dp/B08ZCMGGD9?ref=myi_title_dp