I'm not aware of anyone who guides on stagecoach. If you want to fly fish for them, you might contact a few of the fly shops in Steamboat and see if they will take you out on the res. If you want to huck hardware for them, i'm not sure if a fly shop will take you out
You might also contact the marina store up at the reservoir and see if they know of anyone who guides on the res. They may not be open yet, but their number is on the state parks web site (too lazy to look it up for ya, sorry!). I'm assuming you don't have your own boat. They rent boats at the res as well, so you can always do that. I fish the coach a lot, so you can PM me and I'll try and help you out if you are having trouble finding a guide. Good Luck!