http://www.catskillscollective.cc
These guys run a training camp, guided ride, weekend getaway cycling program from near the Ashokan Reservoir. I've never been, but it looks great. They do guided day rides as well.
There is also the new Ashokan Trail, which looks like nice gravel.
https://ashokanrailtrail.com
Overlook Bikes in Woodstock also do group rides.
https://overlookbicycles.com