Got any idea of the weight of the stuff? Given that it's souvenir stuff press fit(AKA interference fit) wooden dowels will work. How big the dowels need to be will depend on the weight.
Mind you, that stuff cries out to be mounted on spent .50 BMG cases. You can press fit those with the head stamp out and it'll be way more impressive than any dowel. Brass isn't going to bother any of the stuff either.
Oh and the last time I bought a hunk of 1/4" thick Lexan(it's bullet proof and daft as hell but adds to the ambiance.) it was $50Cdn for a 2 ft x 2 ft sheet. Wasn't recently either.
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