I was curious and looked at RockAuto. They are expensive even on RockAuto. Looks like compatibility was the same for most from 90 to 97. If you go to a pick and pull, and they dont have your wheel sensor (eg FR vs RR), you might be able to splice the replacement into your old sensor wire for the same year. Click on the part number and you compatibility
I'm just unlucky. We have 5 or so large pick a part wrecking yards in Melbourne region but current stock is 1998 or younger. More dedicated subaru wrecking yards are closed for at least a few days. Many businesses restart trading on the 8th Jan. There are others around the country but trying local first. Plenty of Forester's, Outback's, Liberty's and Impreza's 98 and younger about. The forester units looks very similar to the outback judging by pictures and it may be that the only difference is the connecting plug.
The old sensors are/were very reliable. And sensitive (requiring tight tolerance manufacturing). And Subaru-specific. They are VERY expensive.
If you can grab one from a salvage car, it's a good way to score a cheap one. However, if there are any corrosion-prone cars/areas in AUS, removing the sensor from the backing plate (rear) or knuckle (front) will usually damage it. The like to swell in the bore and removing it is near impossible.