I've never heard of a gameport to serial
It is possible to connect a number of gamepads to a parallel port. (playstation, nintendo, sega etcetera)
There is a free windows driver and schematics
at this site http://www.ziplabel.com/dpadpro/
There is also a dos TSR whose name escapes me at the moment.
(linux users will find support for parallel port gamepads built into the joystick driver.)
you can get usb---gameport adapters if you need to add a gameport device to your PC. Gameports are nice for DIY as they just use resistance and you can easily make a controller from cheap and easy to put together parts.