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
OFFTEK 32GB Replacement Memory RAM Upgrade for Microstar (MSI) B450 Tomahawk MAX (DDR4-21300 (PC4-2666) - Non-ECC) Motherboard Memory at Amazon.com
R5 3600 Cpu + 16gb Ddr4 2666mhz Ram + Msi B450 Tomahawk Max Motherboard Set Socket Am4 Amd B450 Desktop Mainboard 64gb M.2 Am4 - Motherboards - AliExpress
Top Gaming Set B450 M-ATX Motherboard with 256G M.2 SSD CPU AMD RYZEN 7 3800X 3700X HUANANZHI A600 CPU Cooler 32G DDR4 2666 RAM
MSI B450 TOMAHAWK MAX - BEST MOTHERBOARD FOR GAMING 2020 • Epic Game Tech - PC Builds, Hardware unboxing and How-to Guides