Dark Prince: It takes 25 games as Vikings states to get a rated BKR.
Interesting you don't consider receiving a provisional BKR rating of 2500+ on just four games flawed. I know many on this site that would beg to differ, especially as one can then play and win 21 easy games and obtain an established (unrealistic) BKR.
There has been much debate on this subject in the brainking board.