Yes, Tycho's advice is spot-on. DNN Corp will be an option again, if they can consistently respond to inquiries. However, our clients (all but one) have migrated to the open-source version you're referring to.
As far as support goes, there are numerous options from the community/ecosystem. I invite you to go to the Agencies page to find some companies you think might be a good fit, then interview each. :)
By the way, depending on where in the world you are (and budget), you can interview some companies face-to-face in the upcoming DNN-Connect conference. (This one is in EU, but there's another one in the US in the early spring/late winter.)