I want a MacBook Pro that runs Snow Leopard. I think I need an early 2011 MacBook Pro to be able to run Snow Leopard. Where can I get a new or refurbished early 2011 MacBook Pro. I don't think a later model will allow Snow Leopard to be installed.
Apple lists all software versions that run on models here:
So you could focus on models that shipped with Snow Leopard and perhaps look at even older models that meet the minimum system requirements for Snow Leopard.
In addition to the Apple pages that bmike has mentioned, you can use Ian Page’s free Mactracker application to see both the earliest and the latest operating systems that every Macintosh model can run.
Mactracker confirms that the MacBook Pro (17-inch, Early 2011) is the last MacBook Pro that came with Mac OS X 10.6.x “Snow Leopard”, and that all MacBook Pros previous to that one can also run it out of the box.