Hi Tom,
If you have any trouble getting your X8R downgraded to the v1 firmware, please feel free to reach out to me.
I work for FrSky in the US office, you can find me on Facebook also under "FrSky Ben", or feel free to message me directly here.
As others have mentioned, your radio is likely on older v1 firmware, and any receivers you buy new will be shipping on V2 firmware.
Be sure to flash your X8R with the "FCC" version since you are in USA you are likely on FCC version radio also.
And yes, X4R have been discontinued for a long time, so pretty much only way to find them would be second-hand market.
Lastly, if you buy any of the newer 'ARCHER Plus' receivers, they -will- work with your radio, but they only support v2 firmware, so you'd have to update your radio to v2 as well as all your older\existing receivers that you have (and rebind them)
Just let me know if you need any extra help with it.