NYSDOT has planned a bunch of state bicycle routes, and has actually published maps of three of them. I tried googling for them, and they seem to be a pretty well kept secret, but I suspect you can get the maps (for free?) if you call
518-457-8307.
At any rate, the "Southern Tier" map is one of the ones that's out now, and it will help you.
Is it Metro North that goes to Port Jervis, or NJTransit?