Hey Springfield, I live in Bloomington — so I'm familiar with the weather!
Two recommendations.
Sierra Trading Post is usually a good bargain and they have a Columbia 3XL vest:
http://www.sierratradingpost.com/col...colorFamily=01
Another good source for 3XL sizes (jackets, but no vests right now) is one of the BF advertisers:
http://store.aerotechdesigns.com/bigandtajaan.html
Happy commuting in the Land of Lincoln,