Steinway has their "Steinway Artist" program [0]. Many top pianists elect to be a part of
it if only so they can ensure a good Steinway to be available at almost any venue they go to.
Other manufacturers have similar programs, but their inventory isn't as widespread or predictable.
Some pianists like Herbie Hancock or Angela Hewitt elect to fly their piano with them everywhere. (They both happen to have Fazioli pianos.)
You mean supplying a concert grand at the venue. Very, very few pianists can afford to do what Gould did, namely, bring it with him.