If you want this kind of work approach the high end private shops they will put you in contact or at least take your details to pass on to the designers they use( which they may or may not do).
We did an art gallery in Kings Road once which led to all manner of contacts, these people only work on 'who you know' they very rarely look up and search for carpet cleaners it will be who ever does Tarquin & Jemima's carpets that they will use.
In the past having worked with lots of interior designers, the work they pass to you can be challenging, we once had an apartment which had leather floor covering, thats fitted leather flooring
which they wanted cleaned also paper rugs, now that is a challenge.
In Chelsea near Sloane Street we did a house which had underground parking it was amazing never come across it before, any way the entire house had white carpet, white furniture white curtains sounds crap but it looked fantastic.
The owner was a well know interior designer who hardly ever stayed there but because of pollution wanted the housed freshened up in the Spring.
As mentioned you have to be confident, proficient and patient the designers can be right ponces, they will mess you about ,get you to jobs only for it not to be done for one reason or another, tell you one thing and its another, grossly under estimate the work involved (in terms of time and effort not money) and demand an immediate appearance despite what you have already booked in.Apart from that they are lovely
Seriously get in with a few designers and once you have their trust they will not use anybody else and cost will not be a barrier.