Shields has no water close by. You would be about half way between High Meadow Springs and Trail Fork Springs. Both have loser flow than other creeks on the mountain, but tend to run reliably most of the year.
High Meadow Spring will be on the way to San Gorgonio (if that is part of the plan) and will take you on a side trip down to the camp and then down further to the meadow where the spring runs.
Trail Fork Springs can be difficult to find the water flow. Years ago someone shoved a pipe into the spring and it has since become clogged, so people see no water coming from the pipe and they declare the spring to be dry. Meanwhile down in the gully below that spot, the water does emerge from the ground and flows down into what becomes Forsee Creek. It does take some hunting but I have been told by patrols in past years that it has been running well into the fall, even while others were saying there was no water. Look on the map to see where the creek goes and it should help you find it.
If you are getting there by way of the Forsee Creek trail, plan to also take advantage of the water at Jackstraw Springs as a possible failsafe.
Hope that helps