There was a product called Opti-Gun that was purported to interface arcade light guns, but I'm pretty sure it turned out to be vaporware.
I think some members here even placed orders and never received the product, so we'll never know if it worked...or existed.
A google search came up with a few similar products, but you have to be suspicious when they don't even have a picture of the product.
http://www.r0r3.com/productsusbopticalgun.htmYou could gut them and install Aim-Track modules, but would probably be better off just selling them and using the money to buy something else.
EDIT: Found the OptiGun product page:
http://www.nanotechent.com/opti-gun.phpExactly what you need....if it exists.
You might try putting OptiGun in the subject line to get the attention of someone who might know something about it.