As in “pa” and “rents.” English sound rules essentially prohibit a schwa being the only vowel in a word, even a short word recently derived from a longer one.
(Another way to put this is: All one-syllable words stress that syllable.)
“Zah” and “rents.”
Well, not all. Often, certain common, little words like “the,” “of,” and “an” are spoken with a schwa.
There’s a pair of fancy pizza places in Boston named Za. I’d never heard the usage before encountering them.
Mentioned in post #7. 
I’ve only ever seen them in print, and mostly, “rents,” and rarely, “za.”
Worked at two pizza places in the late 80s and early 90s on the west coast, and I don’t recall a single instance of anyone saying “za” around me. Definitely regional.
I also worked for multiple locations of two pizza places in the late 80’s into the early 90’s, and I never heard the term until I read Snow Crash maybe 10 years ago. I thought it was “future slang” that the author made up. When I first started playing Words With Friends I discovered that “ZA” was an accepted word, but it still didn’t click. Had to look it up.