This is a skill far too few SPs possess! For those of us who enjoy lengthy orgasms, there's few things more frustrating than a girl who leaps off after the first spurt.
The only girls I can recall seeing in recent memory who will happily keep sucking as long as you want are Scarlet Slut, Laylaloulou, and Kara at Genesis II. The first divides opinions looks-wise, the second is terribly unreliable with comms, and neither fit your busty criteria I'm afraid. But all three give fucking fantastic oral.