Which is correct? "While supplies last" or "while supply lasts?"

For marketing copy, is it correct to say "while supplies last" or "while supply lasts?" I've most often seen "supplies last" but I suppose "supply lasts" could be correct, too, depending on how you interpret supply as a noun - as in "we have a supply of items" versus "we have supplies of items."

Solution 1:

'We have a supply of items' is fine and is in the count-mass grey area (?/*We have two supplies of items.)

'While supply lasts' is forcing a more mass usage on this sense, which sounds unnatural.

'While our / the / this year's supply lasts' sounds less outlandish. 'While supplies last' is by far the more usual non-determiner(etc)-accompanied usage.