Horatioo, certain "government agencies" might try something like that, but I guarantee you, the US Military would not stand for it.
They are the single largest procurer of both firearms and ammo. To place them at the mercy of some other nation and what they thought of how our military is told to perform their job, by the same legislature that restricts their procurement methods... Strategically and tactically, it would be a non-starter.
On the other hand, for the BIG manufacturers to stop selling to domestic LE, would affect their bottom line, but only in the short-term. In the longer-term, it would protect both their LE accounts and their civilian accounts (which are much smaller than LE sales, but are a significant portion of their sales, regardless).
To that end, we really need to write their boards of directors and CEO's, outlining the effects of such a strategy. Would companies like Glock and Sig follow us? Who knows, if we don't attempt such a campaign.
I do know, that if the BIG arms companies aligned themselves with the civilian market, LE would raise a stink the various legislatures would not be able to ignore.