I think the OP will be much better served by directing the question towards an employee at a Jewish pharmacy. Many of them are very knowledgeable about vitamins, and some pharmacies even have a vitamin specialist who really knows the distinctions between the brands.
For example, Refuah Pharmacy in Lakewood has an employee named Isaac who is a tremendous expert. (IINM, there is even a dedicated option on their phone system to reach Isaac.)
In BoroPark, there's Landau's 5201 13th Ave, 718-851-8809 that's knowledgeable about supplements.
