Best place I have found for Winnebago parts is: lichtsinn rv.
They have a facility about a mile from a Winnebago plant in Forrest City, and can get any part for any year and model of Winnebago. (so they say) Price seems reasonable, too.
I replaced the pass. side mirror on my old 1997 Itasca Sunrise about 4 years ago. Mirror is not heated but is remote-controlled. Paid $135.40 plus tax, but as I say that was 4 years ago.
Not that hard to install.