Where would they come from?

The Britishicon weren't likely to let a stash of modern rifles in the hands of the Arabs. I don't recall the Germans actively recruiting the Arabs either so they wouldn't have given them to them. Captured weapons would have been removed, the Germans would have evacuated the rest.

Doesn't mean there wouldn't be a few out there but to have enough to advertise them nationally?

Could be Israeli rifles, who knows. I do recall reading somewhere, perhaps here on this forum, that rifles which served in the desert lack their finish as it was blasted off by the sand.