Oh, @Hugh_Glass, I wish I would have known of this issue before you sent out your packages.
If you used the vials that our friend @Tappy sent out with his Afghani x Blue Lights gift seeds, they will fit in a standard envelope and make it through the US mail system. For extra security and stealth, you can tuck one little vial in each opening at the edge of a standard piece of cardboard, then tape it in place.
Here’s a picture of the vials @Tappy used (photo by @TheShowMeHomie). I’m not sure of the size, but these types of vials are dirt cheap.
Sorry for this extra and unexpected cost, @Hugh_Glass. You were already so generous! Thank you very much!