sorry, the original db15 IBM game port and the USB are two uttery different generations and types of interface.
USB is a digital serial interface that transmits ones and zeros, while the IBM game port is a medieval torture implement that samples potentiometer positions in a joystick or simply, whether a normal push button directly attached to the cable goes "click".
So, that whole affair is not like catholics and protestants, it's more like catholics and algae.
What would be feasible, like anything it: Take a programmable system like the Raspberry Pi, attach the USB device, have the Pi simulate the behavior of an old school game device.
Or, that basically would be called an "active adapter". Those possible exist already and if they do, they're dirt cheap.
But, less likely than the opposite, meaning USB adapters that will allow people to use their legacy game controller or keyboard.
Alternative: Well, Windows does USB, get drivers for that pad?
Or, gamepads with "buttons only" so no "analog" joysticks but mere arrow keys, are really, really simple. For the game port, you could build one yourself with some push buttons, a swiss army knife and chewing gum. Or buy one.
Or, rather certain that the ones from the 8 bit console era like Nintendo NES are just as simple and could indeed be adapted to PC.