Neil
You could do either/both. But if I was you I'd firstly put together a good company info pack to include an introduction letter with the work your offering, t&c's, insurance details etc etc. Then I'd walk around the LA's introducing yourself and ask to speak to the person in charge of dealing with all cleaning issues (usually the Maintenance Manager).
If they are not available, ask for their name and number etc and leave your info pack (along with your buiness card) with the person you spoke to.
If you hear nothing after a week or so, give your new contact a follow up call.
Richy