Any of these boards should work: http://bootgod.dyndns.org:7777/search.php?ines=18
Especially all of the JF-24A boards.
Shipping from Japan usually is cheap.
http://kevtris.org/mappers/nes_custom/NES_21G_CPU_72P.html
This is what I found. Looks like an NROM board except with a RAM instead of CHR-ROM plus many other components (diodes, resistors, 7404, 74138, 7432, 74374), perhaps for PRG banking?