The climb gradient for the B737-200 basic, as well as the -200ADV (and all the other series 300, 400, NG), is the same: 2.4% climb gardient.
And the relationship is:
Climb gradient=(R/C)/(V*COS GAMMA)
Being:
R/C = Rate of climb
V = True airspeed
GAMMA= Flight path angle realtive to the horizon
This is a simplified formula and of course the uniots must be consistent to obtain a valid value.
I hope this helps
I almost forget what fruitbatflyer mention, the values are in graph form in the AFM, in the Chapter 4 of these manual you have a lot of graphs dealing with the climb gradient for 2 segment and third segment for the engine inop case.
I canīt remember if there is a number published for this value in the Ops Manual or in the FPPM.