You can already buy TeamGroup's DDR5 memory kits on Amazon and Newegg | TechSpot
Corsair Vengeance LPX 32GB (2 X 16GB) DDR4 3200 (PC4-25600) C16 1.35V AMD Optimized Memory - Black at Amazon.com
Timetec 32GB KIT(2x16GB) Compatible for Apple DDR4 2666MHz / 2667MHz for Mid 2020 iMac (20,1/20,2) / Mid 2019 iMac (19,1) 27-inch w/Retina 5K, Late 2018 Mac Mini (8,1) PC4-21333 /PC4-21300 MAC RAM at Amazon.com
Amazon.com: Corsair CMK32GX4M2A2400C16 Vengeance LPX 32GB (2x16GB) DDR4 2400 (PC4-19200) C16 for DDR4 Systems - Black : Everything Else
G.Skill Trident Z NEO Series 32GB (2 x 16GB) 288-Pin SDRAM DDR4 4000 (PC4-32000) CL18-22-22-42 1.40V Dual Channel Desktop Memory Model F4-4000C18D-32GTZN at Amazon.com
Amazon.com: Corsair CMK32GX4M2A2666C16 Vengeance LPX 32GB (2x16GB) DDR4 DRAM 2666MHz (PC4-21300) C16 Memory Kit - Black : Everything Else
parts-quick 32GB (2 X 16GB) Kit Memory Module for Apple iMac 27" 2017 5K Retina Display DDR4 2400MHz SO-DIMM Compatible RAM at Amazon.com
G.Skill Ripjaws V Series 32GB (2 x 16GB) 288-Pin SDRAM (PC4 21300) DDR4 2666 CL15-15-15-35 1.20V Dual Channel Desktop Memory Model F4-2666C15D-32GVR at Amazon.com