Must agree with Kevin that H. opuntia is the easiest to deal with.
Also need to agree with crimson that a local reef club is the best source. Halimeda's don't always enjoy being shipped, repeatedly exposed to air, and manhandled in general. In the LFS it's probably a combination of those things in addition to a lack of carbonate alkalinity.
That said, Inland is as upstanding a place as you'll find...IMHO.