Yeah, Supermicro only makes EPYC 3000-series boards in Mini-ITX. Doesn't look like ASUS, ASRock, Gigabyte or Tyan make any EPYC 3000-series boards, either.
Otherwise, there's Ryzen (AFAIK, only Ryzen Pro officially supports ECC, but apparently it works on the regular ones, too), or a (probably...