okay, this is an update for anybody who's out there trying to convert these controllers still...
The HD15 vga cables (at least the ones i've found) aren't going to work anymore. There are actually only 12 wires running through them now because the shielding and insultion (or something like that) are used for the 13th and 14th wires, so it's really not practical to use them anymore.
However, i did find that the DB15 cables actually use 15 individual wires running through them. They have a different shape and it might be more difficult to mount it into the memory card slot of your duke controller, but it should still work non-the-same!
the cheapest place i found the db15's was at http://www.cablewholesale.com/
. So if anyone's still trying to mod these controllers this late in the game, heres an update.