McKinsey takes a handful, usually less than 8, for the larger offices. By contrast, for full time, they have around 30 BAs in those offices.
Bain and BCG take from 2-10 interns an office. By contrast, Bain has 25-30 ACs in the larger offices for full time. At BCG, the numbers are slightly less.
This goes to show that it is VERY difficult to land internship positions as summers, but the prospects for full time undergrad recruiting are easier (though comparably to finance still difficult).