google search it...
http://www.artsuppliesonline.com/catalog.cfm?cata_id=366
http://www.rexart.com/liquitex_acrylic_mediums.html
http://www.misterart.com/store/view/001/group_id/2272/Liquitex-Acrylic-Flow-Aid.htm
http://www.texasart.com/store/view/001/group_id/2272/Liquitex-Acrylic-Flow-Aid.htm
Start here...
Regards...