You can try the script "js_Select notes by notation keywords".
If a note has notation information, REAPER stores this information as easily readable text inside a MIDI text event. For example, a note in channel 1 and pitch 64 that is notated in the high voice in the top staff will carry notation text "NOTE 0 64 staff 1 voice 1".
(To figure out the code that REAPER uses, open the "Raw MIDI data" window, which will display all notation text.)
This script selects notes by matching user-supplied text with the notation event's text. In your example, just enter "staff 1" and "voice 1".
There is one snag, however: Only the notes that are *forced* into the top staff will carry the "staff 1" info. You may therefore need to tweak the selection using the MIDI editor's built-in Filter.