Because they never officially released them.
For the uninitiated, MCPX (often associated with early Intel “McPherson” chipsets or certain NVIDIA MCP (Media and Communications Processor) variants) isn’t your standard BIOS. It’s a proprietary, low-level bootloader that initializes memory controllers, SATA links, and critical PCIe lanes before the main BIOS even wakes up. Without it, you’re not reviving that thin client, legacy industrial PC, or prototype motherboard. Download Mcpx Boot Rom Image
Open your emulator and navigate to the or System Configuration menu. Locate the field labeled MCPX Boot ROM Image (or similar). Because they never officially released them