IF it has 7 courses, it is already the XTRA. Regular 05 only had 5 courses.
Unfortunately nobody has cracked the gamecode yet as to make a bootleg upgrade kit.
There are NOS conversion kits out there.. but the problem is that it requires you to phone up to it via the phone line, but it does not support the complete anymore, so, even with an original kit its no god unless you can figure out how to fake that phone call.
IIn reality you would need to figure out what board is in there(green or red) and get the corresponding complete board and drive. It makes a difference because the red board uses an atx type supply and 30 some pin power connector, the green uses a regular type supply and gets power through the jamma edge connector.
Theres a couple sellers on ebay and last time i shopped it was around the $350 range for the cheapest.