active.com is a good website to search for running and cycling events, you can search the type of event, the state, and the month range, and it will let you know a summary of the event and usually a link to the event website or at least you can google the event name.
I know MS used to do an MS150 in southern central Wisconsin. It was my first multiple day ride and was a blast. Cow-a-Lunga also does a charity ride in south eastern WI. I seem to recall that they are a bit more costly as far as charity rides go though.
Since I do not know where you live in Wisconsin (I live in Oshkosh), and how far you are willing to travel, my best advice is to go to GOOGLE and type this phrase: cancer charity cycling rides in wisconsin It came up with several his for you to follow up on.
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