It looks like the control box is an "Airtech 40ci" (not "ic"). One assumes it is the software for the control box that is needed.
I note from Pitsco that they sell through resellers. Many of those resellers may have been in business for many years - have you tried reaching out to every one of them? By phone and not email?
I'm seeing lots of these tunnels in Google searches (a lot being sold off, mind you, many of them by US school districts!).
There seems to be a version of the tunnel with a similar instrumented platform to yours, but with a more simple readout unit: see https://www.ebay.com/itm/173594174852
My experience with devices like this (used to run a lab a long time ago, bought masses of National Instruments kit, built interfaces and so on) is that the kit is usually least-effort. The data rate won't be huge, because you're looking at more-or-less steady-state effects, and the PC data capture rate (even back in the day) will have been adequate so there probably won't be any buffering / storage on the "interface." So the output to the PC is also unlikely to be heavily multiplexed.
Is the output on your device a 15-pin "game port" or a 9-pin serial port? If a game port, one has to assume that they're just throwing pretty simple data down the interface (similar to x/y/z joystick data) just like a game controller would. Have you tried firing up some simple data logger code attached to the game port card you bought?
A PC game port is designed to capture 4 separate analogue levels + 4 digital (button) inputs. That sounds about right for the device you're talking about. My best guess on this limited data is that the "interface" is simply converting signals from whatever comes out of the tunnel plate to a range the PC game port can handle, and little else.
This article provides more useful information about the game port: https://www.sciencedirect.com/topics/co ... pplication
Basically the analogue pins are expecting to see a varying resistance. Per that article, Qbasic (for those of us old enough) contained commands to read the pins directly. So you could roll a bit of code, plug in the controller, tweak the tunnel platform and see what happens! Then all you need is to do some calibration... (well, almost).
With a bit more searching, there might even be something pre-built (perhaps for Linux rather than Windows, but you can always find a way to get that code running through Virtualbox say on the PC or some other route) stuff out there you can use or adapt quickly with a nice GUI
The other approach used by some in the modern world is to do the analogue reading on an Arduino then pipe that to the PC, but since you've gone to the trouble of getting a game port card then I'd be inclined to keep going a bit with what you have!
I know it won't be "the software" but I suspect it will take no longer than trying to track down the elusive kit you seek. There are quite a few manuals for later versions of this tunnel I've found available via some advanced Googling. Does yours also have a manometer port, and do you have the manometer?
Good luck. Happy to help a little to get you pointed in the right direction.