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
Corsair Vengeance RGB PRO Series 128GB (8x 16GB) DDR4 3800 MHz CL19 - Memoria PC Corsair en LDLC | ¡Musericordia!
16GB G.Skill Trident Z Neo DDR4 3800MHz PC4-30400 CL14 RGB Dual Channel Kit (2X 8GB) at Amazon.com
High Latency on 3800 MHz CL16 RAM With Tight Timings (B-Die) : r/overclocking
Corsair Vengeance SODIMM 32GB (4x8GB) DDR4-3800 (PC4-30400) CL18 for Intel X299 Systems - CMSX32GX4M4X3800C18 at Amazon.com