The case is not sold separately however as long as there is no physical or water damage done to the case or the buds you may be eligible for an exchange for the buds and the case.
Call Samsung and as long as you have your proof of purchase you can get a replacement Earbuds. all you have to do is send them back the old earbuds or the old case and there send you a new case with new ear buds
I also lost my galaxy bud charging case. Can I get a new replacement case or buds? I have the box that they came shipped in and also the shipping confirmation when I originally received them from Samsung.