Do you need RDIMM/LRDIMM or would ECC UDIMM suffice? If the latter, have you considered a Ryzen 3950X or a Threadripper 3960X? There are plenty of X570/TRX40 motherboards that properly support ECC UDIMM (but there are also some that don't).

If you need RDIMM/LRDIMM the only current AMD alternative to EPYC is the recently announced Threadripper Pro. Launch partner is Lenovo with the ThinkStation P620 where you can get 12-64 cores with up to 1 TB of RAM. Expected to be available in September.