Check in with Grant at the Estes Angler - He knows the park extremely well. I live near RMNP, and make it a habit to stop in his shop every time I fish there.

Best bet would probably be the Big T in Moiraine Valley, but it can be kind of crowded. You can pick up the odd cutt at the alluvial fan, but you should plan on a hike-in fishing trip for the best park waters.