I don't know of a spreadsheet, but I'd just use the church's calendar system for this.  All you have to do is enter women's names once, and set it to repeat every 3 months.  *poof* all done.

If you're looking to track actual visits instead of just creating a reminder system, you would export all the sisters' names from MLS as a comma separated file (ask your unit clerk -- if he can't do it, tell him it really can be done and get him to find someone who can help you).  Import those files and then enter the dates visits were completed in successive columns.  If you upload your spreadsheet to Google docs every member of the presidency can update it.