If you haven't already, try Old Lady Gibson at the scrapyard NW of Novac.
I did. She had none.
The place vendur pointed out had some, though - Four in total, indeed! Proved to be sort of in vain though - the unmarked quest to fix the Food Sanitizer (or whatever it's called) at Camp McCarran appears to be broken, as it keept telling me that I didn't have all the parts on the list to fix it, despite that I actually had'em all
. Fortunately I could still fix it thanks to Jury Rigging though...