Bilstein seems to be the only aftermarket struts of any brand I could find anywhere!
I can't find quick struts anywhere for your WRX, so you will have to deal with spring compressors
If you drive the WRX like a regular car, 100k on Bilstein is nothing, and you might be able to do another 100k on them, by which time there will be more struts available.
I found these OEM take-offs
for $450 for the set of four. Probably the best deal
KYB seems to be the OE supplier, but they don't sell any aftermarket struts for your car