Title says it all. Where do the tract builders get them? I know they must pay less than the $800+ I'm seeing online... Thanks!!
Call your local glass companies. With a short notice they can cut you a large mirror to size.
As rjr220 said, call your local glass company.
A few years ago I was looking for a frameless 1/4" mirror with polished edges measuring approx. 32" x 42". Bathroom design house wanted $250. Local glass shop charged $45.
You might also try Craigslist or your local salvage stores. I frequently see them listed on CL after someone has removed them during a reno for little or nothing.
First one I came across searching "large mirror":
Large bathroom mirror. 3' x 5'9" Perfect condition. Just remodeled bathroom. $15
another one was listed as an 80" x 60" wall mirror - $25, although I have no idea how you would transport it???
Here is a link that might be useful: CL ad for mirror