hmm, i don't know of anywhere on line but if you have any orchards near you or orchid breeders they should have some and i'm probably thinking it would be cheap but i'm not sure
http://www.boasandballs.com/supplies.html
well those were the two I have. The one from boasandballs you can get bigger bags up to 23 lbs not sure what shipping is. You could check with your local green house. Thats where I get mine if I cant find it at the loca walmart.