To purchase PLR products that allow you to pass on the PLR rights and source files to others, you should look for platforms that specifically offer Resell Rights or Master Resell Rights (MRR) products. These are websites that specialize in providing products with resell rights that enable you to sell the products and pass on the rights to your customers. These platforms offer a variety of digital products with different licensing options, including MRR, which allows your customers to resell the products as well. By choosing products with resell rights, you can build a profitable business by selling digital goods while granting your customers the opportunity to do the same.