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.

Thank you everyone for your suggestions.

@facten I forgot all about Uline.

@ghdprentice I know exactly what expanding bags you are talking about too.

@tcotruvo Oddly enough, PSB could only provide the new boxes. They did not have any foam inserts to sell me. That still has me me scratching my head.

Another "custom-made" option might be the styrofoam "popcorn" packing used to protect fragile items during shipment.  It is extremely flexible as far as fitting into every nook and cranny, and is surprisingly strong once packed in tightly.  I have a bunch of it I'd love to recycle, but unfortunately, I'm up in Canada.

I’ve shipped heavy speakers around the world. No issues, thank goodness. 
I buy 2” styrofoam foam from H Depot and cut to fit. 
 Ain’t Nothing Like The Real Thing- but it works in many situations. 
Good luck. 

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.