May be here: (not tested)
http://retrolandia.net/foro/showthread.php?tid=75

VHDL code (source of ZXMMC) exist, but old slow version. ZXMMC and DIVMMC use identical access to SD card. Only numbers of both I/O ports are different on DIVMMC. I plan implement DIVMMC in my new MULTIINTERFACE, but this is now in development, need time.