Actually, it is in Part 61 where recent experience is addressed. Note it is specifically for "pilot in command". Note also that 61.57(2) specifically excludes PICs employed by an air carrier operating under Part 121. You can read the references to Part 121 listed if you want more info.
Sec. 61.57
Recent flight experience: Pilot in command.
(c) Instrument experience. Except as provided in paragraph (e) of this section, no person may act as pilot in command under IFR or in weather conditions less than the minimums prescribed for VFR, unless within the preceding 6 calendar months, that person has:
(1) For the purpose of obtaining instrument experience in an aircraft (other than a glider), performed and logged under actual or simulated instrument conditions, either in flight in the appropriate category of aircraft for the instrument privileges sought or in a flight simulator or flight training device that is representative of the aircraft category for the instrument privileges sought--
(i) At least six instrument approaches;
(ii) Holding procedures; and
(iii) Intercepting and tracking courses through the use of navigation systems.
(2) For the purpose of obtaining instrument experience in a glider, performed and logged under actual or simulated instrument conditions--
(i) At least 3 hours of instrument time in flight, of which 1 « hours may be acquired in an airplane or a glider if no passengers are to be carried; or
(ii) 3 hours of instrument time in flight in a glider if a passenger is to be carried.
(d) Instrument proficiency check. Except as provided in paragraph (e) of this section, a person who does not meet the instrument experience requirements of paragraph (c) of this section within the prescribed time, or within 6 calendar months after the prescribed time, may not serve as pilot in command under IFR or in weather conditions less than the minimums prescribed for VFR until that person passes an instrument proficiency check consisting of a representative number of tasks required by the instrument rating practical test.
(2) This section does not apply to a pilot in command who is employed by an air carrier certificated under part 121 or 135 and is engaged in a flight operation under part 91, 121, or 135 for that air carrier if the pilot is in compliance with Secs. 121.437 and 121.439, or Secs. 135.243 and 135.247 of this chapter, as appropriate