Have you considered SW Wisconsin? Rich Osthoff has a great reputation. I'm sure fishiowa will see this thread and comment. He has hired Rich a number of times. He may have personal experience with Iowa guides too but I'm not sure. And yes there are definitely IA guides that operate out of the Decorah area.
I'm not sure where you are located and if you are locked into Iowa or if you are open to other parts of the driftless. If open I would agree with IATrouter and Larry and give a+1 on Rich Osthoff and SW Wisconsin. Rich does the traditional guide thing and although I have never fished with him that way, he knows his stuff and the SW WI waters well so I wouldn't hesitate to recommend him.
What Rich offers for experienced fly fishers that is unique is called split fishing. You split the fishing time; so yes, he is the guide but he not only carries a rod but also fishes roughly half the time. To paraphrase from his description, you fish where/how he would fish if he were fishing alone. We have ended up in some pretty interesting places and if you pay attention you can pick up a lot from just watching how someone with that level of experience fishes.
If you are a beginner go the traditional route and as a retired teacher he will show you as much as you can absorb. If you are an experienced fly fisher and in decent shape (Rich is a very strong hiker) go the split fishing route.