You can try EBay seller "aquatic6414". They sell pairs of marimo balls and have flat shipping - which is good if you want to buy other plants from them too. I bought corkscrew vals, anacharis, marimo balls, and giant hygros from them - all are still doing well, except the hygros (but they all arrived in good condition).
I'm guessing the hygros did poorly because my lighting sucks and because the hygros were grown emersed (which is stated in the EBay listing).
25g Marineland Eclipse (30w T-8 ):
- java ferns, anacharis, corkscrew vals, giant hygros, marimo balls, java moss
- zebra danios (5), otos (2), others TBD
6g Marineland Eclipse (8w T-5):
- anacharis, asian ambulia, java moss
- white cloud mountain minnows (10 = 6-7 inches total)