I don’t have a reliable source for you (I am searching, too), but these earlier discussions might offer some suggestions (the second link may not seem to be about pita, but is, and subsequent posts in that thread do have pita information):
I wrote to Bonapita in Boston a few months ago asking if they sold their pita separately and they replied that they did. I haven’t tried them yet but they are in the list of places to try soon. Their pita is house-made. It seems that they are closed on Sundays but you probably wouldn’t want to get them that early anyway.
Georges in Methuen makes and sells their own pita, we like it a lot and
so does Sofra in Watertown. Sofra is somewhat connected to Oleana and Sarma
if you like their pita.
Yes, I know. There was a discussion of the closing elsewhere on HO. I only linked to that discussion here because there was a further discussion of pita down thread there.
On request Greek Corner (North Cambridge) serves fresh for a small upcharge from their usual (presumably packaged) stuff. I assume they’d sell it for take-out.
For packaged pita from I like Arz brand (from Montreal) much better than the others.
Maybe worth a call to Sophia’s Greek Pantry in Belmont? Though I don’t know If Sophia’s can help, I found the staff above and beyond helpful when I visited their Lowell branch a couple weeks ago.
Side note: Like @grumpyspatient, I buy fresh pita in Methuen (though Korbani’s is my go-to) which obviously does not help with the original request.
Fresh Pond Whole Foods carries George’s. I think some of the other WF markets do too, but I use the really large ones as pizza shells and only the Fresh Pond location consistently has the 14"ish ones.
So I made an effort to hunt today. In the area where the FP WF carries local breads, etc. (Iggy’s, Hi-Rise…) they carry the thick pita I mentioned: Angel out of NY (with shortish sell-by dates). In the aisle where they carry their packaged breads, on the bottom shelf, they do have the thinner pita from George’s (with longer sell-bys).