42 commando are the maritime security platoon of the royal marines so they are normally based on ships i also think 47 commando do be based on ships also and i think some from 43 commando are based on ships or submarines not too sure
42 are maritime "specialists" shall we say although there's nothing to say 40 or 45 couldn't deploy on ship.
47 are basically your LCs so yes alot of them will be attached to ship deployments
Hopefully someone knows more than me on this and can correct me and add some information but I read that as part of future commando force there would be a move towards a US marines style amphibious expeditionary force in RN task forces like the carriers and the presumed carrier groups which I imagine would require significantly more marines spending more time on boats.