You are most likely right.
No worries though- when (not if) Trump is the nominee, signs will be available. One may, however, have to purchase a few extra, now and then, to be able to claim them as their own- over the course of the campaign.
One of the reasons I volunteered to collect signs the day after the election, was to guarantee that I had signs in the general election. I went so far as to take the wire frames of other defeated candidate’s signs, for future use, from out of the dumpster used for the express purpose of disposing of unwanted signs.
I have given signs to ALL my neighbors so my sign would remain in my yard!!! Neighbors were ALL very grateful my WHOE street both sides for Trump!!!!