I have someone I know that is well East of me that does that type of opperation.
That kind of work is also for root pruning as well. Where the tree needs to be kept within certain guidelines of growth. This kind of work is mostly done on large commercial. Where astetics(sp) is important and they have the money for that purpose
As far as transplants. Same as above. As well as park applications. Also where you have wealthy home owners that will pay for a 30' tree cause it will fit in well with their landscape.
We're talking the Hamptons on Eastern Long Island. Big $ out there.
There is also a great deal of expertise in digging out and planting trees of that size.