There is/was a limited edition CD of the Bullitt score that contained both the WB LP version and the actual film tracks. It fit onto a single CD. Film Score Monthly, AKA FSM, released it. Well worth picking up.
The tune in question is called "Song for Cathy." The film version is better than the LP version, IMHO.
Lalo also did a re-recording of this music circa 2000, and while it is good, there was too much temporal and geographical distance from the original for it to work as well as it could have. This version is on Schifrin's own Aleph label. Not as good as the FSM, but the price is right.