Corsair Vengeance SODIMM 32GB (4x8GB) DDR4-3800 (PC4-30400) CL18 for Intel X299 Systems - CMSX32GX4M4X3800C18 at Amazon.com
Dirt cheap Gigabyte B450 S2H is surprisingly capable of 3800 MHz RAM at 1900 FCLK (even official site only lists DDR4 3600 as a maximum supported frequency) : r/overclocking
G-Skill Sniper x 3800 mhz 8x2 ram at sahibinden.com - 1120750118