This is the wires I had in behind my thermostat that were run initially at time of build to the basement furnace:
Literally was 6 (sorry i thought 7) wires that were bundled into one bunch. The Arpi's guy noticed this while replacing my fan motor and after re-wiring for me at the furnace and removing the lame setup Action Furnace did, he went upstairs to the Nest, pulled the wires out further and voila...the entire brown bundle was there and he just had to un-strip the brown sheath to see the remainder of the wires for setup.
Seriously I ran that lame setup with the manual fan switch for years until Arpi's came to replace my furnace fan and noticed that. Dude asked me wtf is this switch on the side for? I told him. And he goes wtf cuz there's this brown cable here with all the wires within. He asked if I wanted it re-wired so I can have fan control on my Nest rather than having to flip this switch and I said yes. He did it at the furnace then went upstairs and re-wired the Nest to work properly. Literally smiled when I told him what Action Furnace did and he left. I took the smile as AF are idiots haha.
When you checked, did you have that brown bundle? If so....may just need to be peeled back to expose the remaining wires. If you have the brown bundle then you should ahve all 6 wires that can be used to wire up your system properly.
If you need to run the extra wire, see if Peter the Electrician can come in and run that one wire for you or try Calgary Telephone and Wiring. Should be like $150.