Are cam how many measurements are there to a cam gear?

For example, if I want an adjustable cam gearset for an ej22, do I have to find a set specifically made for the ej22, or a set that just has X teeth, Y thickness, Z radius, etc?

a set that is made for the ej22. I wouldn't mess wiht timing on a subaru. they are electonically timed mechanically advancing or retartding the timing can really do some damage.

Yeah, there isn't much you can do with timing. I think there is only about 20 degrees of adjustment before the ECU throws a CEL. Most aftermarket cams just adjust lift and duration, but not timing, for that reason.

Yep.
For about the cost of a set of gears (which I don't know a single company that makes them for the EJ22) you can get a set of cams from Delta for your car. Less than $150 when ground on your cores...

Since your other post is about thin head gaskets I'm guessing that you maybe wanting to correct your cam timing back to stock after moving your heads closer together.
There other ways to do it other than cam shaft gears, it is not as easy but cheaper. Off set keys, moving idler pullys for example.

Regards John