Ibiquity (ibiquity.com) has a list of 1618 stations currently carrying FM and AM HD, of which 259 are AM as per today (I don't know how old the list is and how often it is updated). I took the liberty of copying the AM list, shuffle the columns a bit to better suit a DX-er, and pasted it into the Google spreadsheet you can access here. I don't know if I have violated copyrights or not; if so the list might need to go away. All of the stations listed are not necessarily running IBOC, and several are probably running IBOC daytime only. I believe the list is of stations that are authorized by Ibiquity to run IBOC.
Unfortunately (for the DX-er, and for the low power station owner nearby), many of the 50 kW stations run IBOC. KSL below is a classic example. Others: WXYT-1270, WTAM-1100, WBZ-1030. The good thing (for the DX-er, not for the low power station owner nearby), is that it seems like a certain signal level is necessary for the digital hash to occupy the neighbouring frequencies. Unlike DRM, which requires very little signal indeed before the frequency is left useless. So a relatively weak KSL will not pollute 1150 and 1170. At least that is my experience.