I get DMSA from vrp.com but since I use Cutler's protocol I only use small doses of DMSA. ALA is the primary chelator in that detox protocol.
ALA is powerful but can be dangerous. The mice in the Gregus study that received ALA *infrequently* excreted more Hg but also ended up with more of it in the brain. Andy Cutler, best known for his frequent dose chelation protocol comments on the Gregus study here. http://onibasu.com/archives/am/74605.html
There are a number of adults in the Yahoo chelation groups who use only ALA but those using DMPS + ALA seem to have the smoothest ride. Cutler touches on this issue in the following audio interview. http://www.healthcentersofthefuture.com/DrCutler/