A garter is an article of clothing comprising a narrow band of fabric fastened about the leg to keep up stockings. In the eighteenth to twentieth centuries, they were tied just below the knee, where the leg is most slender, to keep the stocking from slipping.
In this manner, who buys the garter for the bride?
The answer is: Anyone can buy the wedding garter.
The mother of the bride can get her daughter a special wedding garter. (Maybe the mother of the bride uses lace from her wedding dress to have a custom bridal garter made using the heirloom material!)