Many OSD chips (inserters) separate the sync and blanking signals.
Maxim made a few, for the security industry, which entered Time Code iinfo into the video chain and needed the sync signals to correspond. EDIT: Heres the MAX7456 eval board, but in CHina....
https://www.ebay.com/itm/135132712344
The old eval board(s) are what you want, as the chips, for the most part are obsolete.
I had several, but no more. Great thing about being an EE student with nice professors - they'd sign any Maxim/NSC/TI/Freescale student form. Free chips! (I mostly went for the National audio power amps and the Maxim "DIP of the month" stuff - MAX038, MAX7XX stuff, the pattern generators, the op amps, some Elantec stuff, you name it - 2 sample chips, delivered to your door, free. TI still does the free samples for students, but you almost have to beg them, with a design concept signed by a professor.