Find filenames with certain pattern on Windows command line?

I just answered this on Stack Overflow a couple of days ago. https://stackoverflow.com/questions/15648679/find-text-string-or-part-of-text-with-dot-in-grepwin/15648872#15648872

In your case it would look like:

dir * /s/b | findstr \.r[0-9]+$

Update

The * in the one of the other examples ".r[0-9]*$" also finds records that end in 'r' since the * quantifier means 0 or more.