Unfortunately it is impossible to get rodeo schedules a year or more in advance. Certain large rodeos may list their dates two or three years out but the vast majority or rodeos fix their dates on a year by year basis.
This is because dates for particular rodeos are determined by individual rodeo committees. Committees must submit their dates to the sanctioning body and have them confirmed, and available dates may depend upon a variety of local conditions.
However most rodeos take place a particular time of year and tend to stick to that time. While specific dates aren't available, if a rodeo has taken place the 2nd week of June (for example) for years, it's a safe bet that it will remain at that same time next year.
For those of you traveling and planning trips to particular events in advance, I know this can be difficult but it's not entirely impossible.
For more on why rodeos move their dates, read Why do some rodeos move their dates?