Muscle memory for weapons systems?
This is a broad question that has no real specific answer as there are no specific training sorties dedicated specifically to "muscle memory", let alone muscle memory specific to weapons switchology.  

Military currency requirements exist for multiple functional skills, air to ground attack, air to air 1v1 ACM, Defensive ACM, carrier landings, instrument approaches, etc.  During any and all training events, whether in the aircraft or simulator, muscle memory is reinforced, but it is more of a by product of all the other things going on around it such as flying the aircraft, scanning the instruments, and executing the procedures.

These currency requirements are generally captured in some sort of a training matrix that is maintained by a squadron training officer, who communicates the requirements to the schedules officer.  Both of these individuals report to the squadron operations officer, who has overall responsibility for maintaining aircrew combat readiness.

Intervals between training simulator or flight sorties may vary by type aircraft, skill-set, and where the squadron is in their deployment/readiness cycle.  (i.e. just got back from war, or getting ready to head out?)

The closest thing to what you are asking is what we referred to as "blind fold cockpit checks".  Early in simulator training the instructor would have you close your eyes, then locate certain switches by feel, reinforcing muscle memory to both locate them and identify them by their often unique shape.  

These drills, however, generally focused on switches related to emergency procedure memory items.  And more specifically, to items related to loss of electrical power, smoke and fumes in the cockpit, and other emergencies where vision could be impaired.