You can create a temporary file of source member information from a source file using the cl command dspfd with *mbrlist as information type to an output file. You can then query on output file and see the last used date, which is one of the fields available in the IBM created QWHFDML format, which is created by the dspfd command.
Hope it helps.
Display File Description (DSPFD)
Type choices, press Enter.
File . . . . . . . . . . . . . . > QDDSSRC Name, generic*, *ALL
Library . . . . . . . . . . . > DEVLIB Name, *LIBL, *CURLIB...
Type of information . . . . . . > *MBRLIST *ALL, *BASATR, *ATR...
+ for more values
Output . . . . . . . . . . . . . > *OUTFILE *, *PRINT, *OUTFILE
File attributes . . . . . . . . *ALL *ALL, *DSPF, *PRTF, *DKTF...
+ for more values
File to receive output . . . . . > TEMPDDS Name
Library . . . . . . . . . . . > TJHLIB Name, *LIBL, *CURLIB
Output member options:
Member to receive output . . . *FIRST Name, *FIRST
Replace or add records . . . . *REPLACE *REPLACE, *ADD