I too have one an FS I think, I got the internals swapped out and upgraded the rod to the captured type years ago. Call my friend MARK at Bradis Firearms in Camby Indiana at:
6939 Kentucky Ave.
Camby, In. 46113
He does have the extended Glock slide stops..........I think yours is aftermarked non Glock, Glock only made the type they use now, except for an older G-17, a current one would fit you G-19 fine.
Yours is Austrian marked and proofed, a real oldy but goody, io use a GS prefix G-19 alot.
GLOCKS #1 FAN!!!
"IN GLOCK WE TRUST"