So, you definitely have a problem there. The EJ20H used a different head design than other EJ20s, and the valves used on the H were the shortest valves that Subaru used for any of the EJ20s at 94.0mm. To add perspective to that, my 93 WRX (EJ20G) exhaust valves are a whole 10.6mm longer!
The only place that I know of that you could order them from is directly from Dokuro in Japan. To my knowledge, Dokuro was the original supplier of the valvetrain on the EJ engines, and they can always reproduce anything that they have specs for. They might be a bit costly, but I really don't know. Valves generally aren't that expensive in general, so it might just be the shipping that will cause you grief. Anyway, worth a shot if you're still unable to find anything.
https://www.enginevalve.co.jp/order.html
Hope this helps.