The company that made the clasp did not string the pearls. Very few pearl sellers make their own clasps. Only the big "name" companies like Mikimoto or Tiffany's would have their hallmark on their own clasp. Most companies that sell pearls buy their clasps from a company that makes clasps, so any hallmark would be of the clasp maker, not the necklace maker.
Therefore, it's impossible to tell you who made the necklace.
I agree that they need a good cleaning and restringing, and then enjoy wearing them!