I use the Cost Index to give me an approximation of VMR in the 737 but I am aware that it is taking account of the wind while in EcON mode so isn't exactly right.
Well, it is actually right, because Vmr (max range) is dependent on wind.
On the 737:
For Vmd (min drag, best endurance), use HOLD page to get holding speed. This is close to Vmd.
For Vmr (max range), set cost index to 0 and fly ECON CRZ.
For Vlrc (long rang cruise), use LRC CRZ. (cost index has no influence).
(For info, LRC is equivalent to ECON speed at cost index around 35-ish. Ie, if you fly at a low cost index, say 15 or 20, going from ECON to LRC will actually decrease your range slightly)