If I were in your position I would ask at the local feeds stores. they would know who they
sell feed to and might be able to put you in touch with local sheep owners.
Then, either ask them to contact them or get a number to call.
I would then ask if they would be willing to let you come out to visit their sheep with your dogs to keep them in practice.
Another Idea, would you be able to teach sheep herding classes?
If so, put some flyers out at the local feed stores that you are offering classes on an individual or group basis.
I hope some of these suggestions might help.