Most modern manuals don't have MRC as yet, because the prospect of fuel prices sky-rocketing as they have wasn't envisaged at the time of aircraft entry into service. Most paper manuals DO have LRC.
On the FMC/FMS units that I'm familiar with, LRC is one of the standard VNAV options. MRC does not usually have it's own specific "MRC select" key, but is easily obtained by entering Cost Index (CI) = 0. This is certainly so for Boeing aircraft, and I believe it to be so for Airbus. Standing by for correction from Airbii operators.
Regards,
Old Smokey