Dan Ryder usually has something for a workshop, and there's also usually something up in Maine each year. I don't remember if I saw any of those are going on this year or not. Dan Ryder also has a great big book on drill design that might be worth picking up.
As others have said though if you can find videos on YouTube and watch them for ideas. Sadly due to copyright laws that is becoming harder to catch anything current since less videos are going up than ten years ago.
FloMarching accounts to watch DCI are also handy during that time of year for me.