Seeking a good Itasca parts source

In the grand scheme of things, there probably aren't that many parts you will be looking for that are strictly Itasca/Winnebago parts. There are tons of online retailers for whatever part you might need. Here's one Adventure RV Supply. I've bought a couple of air conditioners from them over the years, among other items.
You can also just go on E Bay and type in whatever you're looking for, and will usually find a number of sources to choose from.