Interior Residential Fire Rated Doors

[Travis Martin]

Does anybody have any knowledge/experience with purchasing and installing fire rated doors for a small multifamily (2-4 units)?  I just purchased a triplex in Lincoln, NE and am doing some minor repairs myself. One of the repairs required by code is that the entrance doors for each of the units need to be at least 60-minute fire rated, but I am having trouble finding a store that supplies this for an interior wood door. Any help is appreciated! Thanks!