Does anyone know of good ringcraft classes in either derry or strabane,

No - don't know any up that way.  You could try and ring Londonderry Canine Association and ask them of any they know in that area.  You can get their secretary's number of the net or from the Kennel club.  You'll also find a phone number for him on showdogsireland.com as their show is being held on the 28th June and it will have a number and address of the secretary also.  If you do find one ensure to post it.  I have a friend who travels from Dungiven to Ballymena to go to a ring craft I'm sure she would be interested in one in that neck of the woods also.

we have one in letterkenny if that would be helpful