You don't say where you are in DR. The larimar is from the Barahona area, mostly around Barahouco. Sounds like you're just looking for the rocks, not set in jewelry???? That would probably be the place to go. Depending on the size your looking for, and if you want them raw or polished.
We saw a lot of roadside stands with bottles filled with larimar stones out there, but they are small.
I bought a couple of those bottles, there are in the small Brugal "extra Viejo" bottles I think they were 400 DOP EACH