Stereo & Electronics - Need wiring help (VSS output wire)

Yesterday I tried to install my new aftermarket Head Up Display unit for my 2002 Z28 convertible. One wire is to connect to the car's Vehicle Speed Sensor output wire. According to search results on LS1tech it seems, that this VSS-wire comes from the PCM's white plug and is colored dark green and white. Unfortunately I don't know so much about engine electronics, so I need your help, please.
1.) the HUD unit's wire now ends under the glove box at the BCM. I think the PCM is in the engine compartment, but of course there must be a wire from the PCM to the speedo. Is there any wire under the glove box, that I can connect to? Please, keep in mind, I'm a total idiot in car electronics, so, to avoid failure, I need an explanation with as much exact information as possible (location, color code etc.).
2.) If there is no way to connect to a wire near the glove box: How can I get the HUD's wire from the passenger into the engine compartment? Please, don't say "go through the firewall", I did read something like this, but I don't know, where the firewall is and how to go through it.
Additionaly, when the wire is in the motor compartment, I don't know where to connect it. I the think, the PCM should be located on the passenger's side near the window. But all I can see there is a lot of wires with two plastic shields 'Do not overtorque', no box with plugs.

Please don't say: let it do by a garage. I'm located in Germany, the next garage specialized in US-cars is about 200 mls away from here and local garages don't have any more clue than I have.

Thanks so much for your help in advance.

Well, you're in luck. Because you have a Camaro rather than a Firebird, the VSS wire is available in the radio harness (Camaro radios have automatic speed controlled volume but Firebirds don't). You can splice into the dark green with white wire in the gray/white 10-pin connector at the back of the radio. The 10-pin gray/white connector and the black 10-pin connector on the back of the radio actually fit together and plug into a single socket so they look like one 20-pin connector. Unplug it from the radio and you'll see that they are actually two separate connectors. There is only the one dark green with white wire in that connector.

You won't need it but if you're curious about your other questions - the PCM is a gray box under the hood on the right (passenger's) side close to the firewall, next to the right hood hinge. It has two 80-pin connectors - one blue and one red. If you really wanted to connect to the VSS wire there you would look for the dark green with white wire in position 50 of the red connector. There are several dark green with white wires in that connector so you would have to be careful to get the right one.

If you remove the two bolts that hold the PCM in place and slide it out of the way, you will see a large rubber grommet in the firewall below it. That grommet is used by most of us to pass wires through to the inside by just poking an extra hole in the rubber. On the inside it is behind the glove box so it's a convenient location.

WhiteBird00, your help is highly appreciated. Thank you for this quick and detailed response. Great Forum!

post up some pics of this set up when you're done.. always been curious how nice you could make an ftermarket HUD in a camaro..