I am not aware of any "easy" solutions to your iron problem.

Do you have multiple springs that could provide the source water to your pond? If they all come out of the same rock strata, then they all probably have a similar dissolved iron content. However, if they come out of different strata, I would suggest taking some water samples for chemical analysis. If one of the springs is significantly lower in iron, then you have already won half of your battle.

I would also let "nature" remove the dissolved iron as much as possible. If feasible, I would build the equivalent of silt-settling pond. Make a small pond with a long, serpentine flow path to capture the spring flow near the source. Your goal is the longest "residence" time possible for the water. Let the bacteria and iron deposits flourish in this pond. You want to have lots of nucleation sites for the dissolved iron to drop out. Existing iron oxide precipitates and bacterial films both serve this purpose. If you can aerate your precipitation pond, that could also be a huge benefit. (Your trout will probably benefit from aeration anyway.)

I would then pipe the flow to a splash pile that is above the water surface of your trout pond. Let the water flow through a big pile of gravel before trickling into the pond.

Good luck on your project!