I recommend Confluence Kayaks if your coming through Denver, they have the gear and guides. Should be able to set you up. I used to work/guide for them so I am biased but believe they run a good shop.
The guide part can be tricky, if the river is permitted, then only guides authorized to work that section are the only ones "legally" able to take paying customers on it.
Ark=Dvorak guides and couple others last time I checked.
Poudre= Poudre River Kayak
Confluence= We guided on clear creek, south platte up by deckers, and would get some permits on the Ark through other companies....
My favorite was you never had paying customers, just some friends out for a float