You might have been expected to travel without one.( the owners manual intimates that) Our 1970 did not come with a carrier either. I have constructed a carrier that accepts a compact temporary use spare, that fits just behind the propane tanks. It took a while to find the proper rim/tire combo with a proper load rating. I believe it came from an early '90s nissan truck product of some kind. A standard spare would not fit in that location without a great deal of modification. Given a few days I could come up with a picture for you if your interested. Others have constructed carriers that hide in the underbelly near the front of the coach...I have seen pictures on this forum, but I couldn't tell you where.
If you don't know where you're going, any road will take you there