Probably the biggest independent source for oil analysis, but a lot of distributors and shops also sell the kits. You mail them off.
If you're going to pull it out of the boat...Might as well clena up the engine bay, think about installing fuel polishing lines, expect to pull the engine apart and do work, as well as sending out the injectors. And replacing the mounts.There's a lot that can be done, and should be considered if the engine is being pulled, but I'd hate to say "pull an engine" before you knew whether it really needed to be pulled at all. Lots of time and money that might not be needed.