There's a campground called "Camp Dick" just up the canyon from Lyons that may have availability.
I'm not sure there is much fishing to be had there, but it's a very nice campground.
To be more exact, it's 14 miles up the St. Vrain Canyon from Lyons to the turn for the Freak to Freak highway. From there it's going to be another 5(?) miles to Camp Dick. All in all, I'd call it 45m for flatlanders.....takes me around 30. I ought to know, it's been my alternate commuting route since the flood (including this week as the roads in Jamestown are torn up)
If you're camping there, I'm not sure about the immediate fishing. But you're about 10 minutes from the Ceran St. Vrain trail, and the water levels have dropped low enough there should be some good fishing there now I think.
And once you're at the Ceran St. Vrain, you're 5 minutes from my front door. We no longer have fish