Honestly, I usually import it from Korea or Japan. The moss is so much cheaper there that even after the higher international shipping costs it's still quite a bit cheaper, especially if you buy several bags at a time to offset the shipping costs.
US vendors of the moss waaaaaay overcharge for it. For example, the typical 100g bag of Besgrow's loose packed long strand premium moss in the US is about $30-$40. One vendor even stocked them at $50 a bag. Same brand, same moss
from Barampung, about $17.
If you're up for buying a compressed bale, it's even cheaper coming out as low as $80/kg for 5A moss.
That said, given the current delays in international shipping, it might take forever to arrive...