Here is the phone number to Heartland: 877-262-8032
It's an automated answer and you will select the option for PARTS (I think it's 2). Make sure you have your Year, Make, Mode and if you have the part # it's even better. I just ordered a door from them and they were very helpful, but I had to do a lot of following up, I'm assuming this is their busy season.
Hope that helps
Edit to add: I recommend you order directly from Heartland if you plan to install it yourself. I priced the door at the dealer and they were going to mark it up 67%.... that's not a typo and that's just for the part, not the labor
.... I ordered it directly from Heartland instead