Latest firmware is available at the main page of the device. In the wiki one can only find older firmware, that still might be helpful. The projects listed below are no longer officially supported. The best practice is to use the EXACT same compiler as mentioned and in most cases the exact same IDE version as mentioned.
Older firmware released by Olimex for MOD-IO2:
1)MOD-IO2 v2 firmware - binary, source, and how-to - click to download
2)MOD-IO2 v1 firmware - C source and HEX for I2C control - click to download