Bicycle production/sales figures? Is there a way to find out how many of a particular bike model were produced and/or sold?  
For example, "how many Schwinn LeTour bikes were produced in 1979?" The Schwinn LeTour question is just an example--I'm hoping to find a website or search strategy for finding this data for any arbitrary bike model.

I often enjoy looking at used bikes (and sometimes buying them), and I speculate that knowing production numbers would a few advantages:


High-production bike models might be more likely to have OEM parts available for a long time.
High-production models may have more rants/raves/discussions on web forums, which can give indications of reliability and build quality. 
If enough data is available, it'd be cool to sort a big database of bike models by "highest to lowest production."


Note: by "high production model," I just mean "many examples (tens of thousands?) of this bike model were manufactured." 

Production numbers for cars are generally easy to find (Wikipedia has a lot of them), but this question has been much harder to answer for bicycles.
I can only answer on the second bullet point of your question:

...may have more rants/raves/discussions on web forums...


Instead of infering this by the production count, you can directly find out how much discussion is happening for each particular bike model.

A simple way is to use Google. For example:


https://www.google.com/search?q=schwinn+letour gives "About 43,800 results"
https://www.google.com/search?q=schwinn+voyageur gives "About 705,000 results"


That definitely means that you'll find more written material on the internet about voyageur than letour.