Local pawn shops or used luxury recycling companies.
For pawn stores, diamond ring recycling is an unusual thing. Pawn store diamond recycling mainly looks at the 4C standard, at this point the brand of the diamond is no longer important, as for the price, the pawn store will look at the type of pawn you choose and the size of the diamond.
If you buy a diamond ring from a major international brand, for a diamond ring, the brand boutique will recycle your diamond ring, but the boutique won't give you a matching amount of money, they will give you the same price for the same jewelry, such as the same diamond ring or diamond necklace.