[I found out about SG plugs at Synjeco sometime in the mid-2000s but never ordered due to price, not that Synjeco is expensive but that it is subject to European taxes.]
I am getting SG plugs from Synjeco. They are a Swiss retailer so their prices have nothing to do with other European taxes. Provided they are the only ones shipping to the USA as British retailers do not ship anymore tobacco to the USA, they are actually cheaper than the prices in UK or other European countries. Yes, if you compares with the flakes available in the USA they are more expensive but I think it has to do not with taxes but because they know they are the only one shipping plugs in the USA and if the alternative is not getting them, better going through Synjeco which is anyway not outrageously too expensive. And they stand back to their customers, they just replaced free of any charge a plug which arrived with a little bit of mold. I am not associated with them in any way.