I had a difficult time finding OEM replacements, dug through designers discords and found the exact specifications that these designers made their boards for.
Moontower o-rings are:
AS568-263 B50 (NBR) Buna-N Nitrile 50 Duro O-Ring
Unikorn o-rings are:
185mm OD x 3.5mm CS or
AS568-263 S50 FDA Silicone (VMQ) 50 Duro O-Ring (same o-ring but US and China use different naming systems)
Bakeneko60 o-rings are the same specs as Unikorn but the stock ones included from CannonKeys are blue