You can still feel, yes?
There are two was I can see y u approaching this without spending a crazy amount, like $10k+, for development of an additive tool.
1) the first method is the cheaper of the two and required destruction and ingenuity. Take a pair of over the ear headphones. You will be destroying the housing of the side with the bad ear. Mind not to damage the driver or wires. Here’s where your ingenuity kicks in. You are going to need something to hold the driver firmly around your neck. You will most likely need to solder on more wire to allow the driver to reach bending your head to to your neck. There’s usually not that much wire from the factory.
The concept behind this, and the next method, is that you may not be able to hear sounds but you can sure as hell still feel them. While localization on the bad side may not allow you to exactly pinpoint the shooter, it WILL allow you to know something is happening in that direction. With time I assume you will assimilate to the minor differences in the amplitude of sounds the game produces to tell the difference between cars, shots, and even varying degrees of distances.
2) this method is going to get pricey. It’s pretty much the last method but instead of taking the driver from a headphone, we’re taking the driver from a studio monitor. This method allows you to control voltage from an interface to increase how much you would feel. Again, this method realistically will cost you a few hundred dollars. It’s better to try method one first unless you’ve hit the lottery.