Use the "Book" option in the ILL system to request microfilm.
Please be as specific as possible, ideally down to the year or film reel number. Many microfilm sets are dozens or hundreds of reels long, and we cannot order that many at once; if you can narrow it to specific reels the request will move much more swiftly.
Look in WorldCat to see which libraries hold the microfilm you need. Go to those library catalogs directly; they often have indexes to which reels you want. Those catalogs will also indicate whether the microfilm circulates.
Because it takes so much time to skim microfilm and scan, most libraries will send the microfilm instead of make a PDF scan.