Here is a working MSI micro-ATX socket AM3+ motherboard: the 760GM-P21 (FX), also known as MS-7641. It uses AMD's 760G chipset, DDR3 memory, and socket AM3 or AM3+ CPUs up to the FX-830, which may draw up to 95W TDP.
I have tested this motherboard successfully with a Phenom II x4 975 under WIndows 10. I have seen it boot from a USB flash drive and from a SATA SSD. I include only the exact motherboard pictured here, without I/O shield, CPU, RAM, or any other accessories. It does include the mounting base and brackets around the socket which allow you to clip on a CPU cooler.Shipping is free to any U.S. zip code. I offer a 30 day return privilege.