Do you mean mcarthy and stone?
I have done a lot in the past, now I just do one regularly ( 8 weekly)
The fact most only have a budget of every 8 weeks, and access has to be internal for a lot of them as they have balconies etc, I wouldn't look for anymore.
If you can get them at the right price then they are ok, but you need to have all your rams and statements available for them to see etc.
Same with any large contract I think it's hard to get them unless you know someone or are contacted directly.
I was recommended to them and that's how I got the contract. You could try an email to head office on the off chance.