According to CPU World all three Ryzen Pro 5755G, 5655G, & 5355G are OEM/TRAY Processors. That is why you don't see them listed in Retail Stores.
OEM/TRAY are processors that are sold in bulk packages to Manufacturers to be used in their products.
All OEM/TRAY Processors don't qualify for AMD Three year PIB Warranty. The warranty, if bought from a Retailer/vendor, will come from the Retailer/Vendor only.
Most OEM/TRAY Processors can generally be found in sites like Ebay or in a Foreign Ebay type site that sells the processors without any AMD Warranty except the one they themselves offer.