The advantages of a gravity furnace
go beyond retro style. Since they use no electrical
power at all, they are ideal for boon docking. While the gas valve can be replaced, the valves that are available are expensive, and have a different port arraignment. This means that some tube bending will be required to install it.
Duo-Therm Furnace Gas Valve, Replacement 710-201MC
Hey look at that! Walmart sells it.
My preferred option is to locate the exact same valve, on kijiji, in some other furnace of the same vintage. I see that you are in Alberta, me too. I just did a quick scan and only came up with one contender:
He wants $200 for it, but I have seen them for as low as $50. Of course, the gas valve may not work, but Randy Bishop
tells me that he has never come across one that a bit of cleaning would not fix.
That brings me to my next point. The thermocouple is a part that can still be purchased.
Bring yours to a furnace service shop. They will likely have one you can use.