Jeff,
There may be a better way, but just save the program below and run it. It should return the contents of line 10.
The called routine is simply a modified version of *pg.cnv, but serves your purpose of simply grabbing a specific line instead of converting the program.
0050 call pgn+";get_line","PROG1","",10,line$
0060 print line$
0090 end
0500 ! ^500
0510 GET_LINE:
0520 enter prog$,passwd$,line,line$,err=*next
0530 line$="",p$=pgn
0540 x$=lst(pgm(tcb(4)+1)); execute x$(5),err=*end
0550 load prog$; password passwd$; line$=lst(pgm(line)); load p$; goto GET_LINE_EXIT
0560 GET_LINE_EXIT:
0570 exit