G. SKILL Trident Z Neo 16GB (2 x 8GB) PC4-30400 (DDR4-3800) Memory (F43800C14D16GTZN) for sale online | eBay
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