What do pilots operating under FAA 14 CFR 91 have to do to fly in any of the Special Flight Rules Areas (SFRAs)?
The "master list" of special flight rules areas (SFRAs) in the United States is FAR 93 (14CFR93)) - aptly named "Special Air Traffic Rules".

It contains a list of areas with "Special Air Traffic Rules", including the requirements for operating in those areas.

Charts with SFRAs on them include a notice directing you to FAR 93 (and often other helpful information about the SFRA):




In addition to "Special Air Traffic Rules" some airspace with "special" rules may be defined by "Special Federal Aviation Regulations" (SFARs), found at the beginning of Part 91.
The only one I see in there currently is the Grand Canyon National Park SFAR.