I'm not an expert with importation of prop weapons. But, if your vendor of choice can ship the props unassembled, .e.g. sometimes, depending on design, the BFG can come in 2 or 3 separate parts, it may be less wait time. Same for the smaller prop guns; some parts unattached.
From my own experience, I had very little issues getting a DC-15X (came in two parts) and a DC-15s blaster (completely assembled) into the US from Denmark, like zero wait time in customs.