Good news, I just went through this for the 3rd time so I have your answer! Chances are there is not a HUD tag (be sure to check all closets, kitchen cupboards, and beneath the sinks).
In each case, we had to go through the DMV (department of motor vehicles), and believe it or not the police department was able to help with information needed to refinance and/or sell. I believe you are trying to establish ownership, and in most states these homes are considered vehicles so they are registered with the appropriate department.
This might sound strange, but it is what was necessary. They treat your home the same as a vehicle. Hopefully this works well for you, when we tried getting a title company to help it was of little use.