There is no legal camping along the north fork of the south platte along foxton. By far your best option for camping is to drive up to Camp Bailey Fest to party and have a blast and support the event that brings the release. If you don't want to drive 40 mins up to the camp, you could find some camping closer along buffalo creek rd. Its free dispersed camping that fills up quickly on weekends (ie full friday afternoon / night), but its still probably 15-20 mins drive.
A Jeffco sheriff's deputy called me the year before last and told me that a large group of kayakers were illegally camped on the side of the river near the foxton run during Bailey Fest. He made his rounds and ended up telling them to leave at around midnight. I'm pretty sure they will be looking for folks camping illegally this year as well. I'd ask all foxton paddlers to refrain from illegally camping along the river to keep Bailey Fest in the good graces of Jeffco law enforcement. Thanks!
P.S. If you haven't seen the Bailey Fest campgroud... its one of the best riverside spots I have ever had the pleasure to camp at. Awesome! We have enough room for hundreds of kayakers and rafters to camp, so come on up.