Title kinda says it all.

Any idea where it'* located?

Should be under the drivers side of the car,
Before you do any adjustments to the cable make sure the shoes are correctly adjusted, don't assume they have automatically self adjusted as they often don't. You might find that the parking brake is fine after that.
Be warned, these cable adjusters often seize up from lack of use.

Roger.

Thx Roger.

I'll be sure to adjust the rear drums correctly to where the drum barely fits.

I need to replace the master cylinder and bleed everything again, but interesting thing happened. I had adjusted the brakes and the parking brake was tight. then a month later, I re-bled the brakes and noticed there was a lot of slack and readjusted and the parking brake is totally slack. any idea what might be causing this?

If the shoes are correctly adjusted and the parking cable is still slack now is the time to examine the cables and mountings. It is possible that a bracket for the cables has got bent/broken but unlikely.
When the parking brake was tight did you try jacking up the rear with the parking brake applied and turning both wheels with a lug nut wrench?, you shouldn't be able to budge either one if the brake is properly set up.
It could be the cables have stretched but this is unlikely, however if you have eliminated all the likely causes start looking at the unlikely possibilities.

Roger.