I suggest you act now. I was in the same boat (no pun intended) several years ago, but did not act. Now my 83 yo dad's mobility is way too compromised to ever get into a boat again, much less go fishing.
Last year my GF's son and I used: Skagit River Fishing Guides ( 888-6-Skagit)
www.SkagitRiverFishingGuides.com , or
www.SkagitEagles.com . Thet are very nice people, and seem very accomodating. They commercial fish in Alaska during some of the summer, but I think they could steer you in the right direction.
It may cost a little more for your folks, because they may have to put two guides into the boat - one to oar and one to assist. But that would be a small price to pay for their enjoyment