Using Propensity Score Matching to Select a Sample

I have a list of several hundred schools with 65 of them being treatment schools. I want to use propensity score matching to choose the 35 treatment and 35 control schools that are most alike based on some school-level variables. However, the taffects pmatch command requires an outcome variable which we do not have since we have not collected data yet.

I would appreciate any advice on how we can accomplish this without an outcome variable.