Source For Styrofoam Packing Inserts

Probably a long shot but you could try contacting PSB dealers or the national distributor. Normally the packing is necessary until delivery, then most owners want to keep them.

On contacting PSB dealers/distributor, I was thinking that they may have around some used inserts for a set of speakers that they sold. But it’s a long shot.

i strongly recommend against “popcorn”.  It is soft and with jostling in transit - think sitting in a bouncy truck for x hundred miles - it can compress and redistribute. At the end of the trip there may be little left between the speakers and the box at the critical bottom.

2” foam is probably the best solution.  You may also be able to get free packing materials from a local appliance dealer, but you need to be thoughtful in how you use them.