O-rings are commodity items. As long as they are not all stretched out you should be able measure them and purchase new ones from a industrial supply house. Get a pair of calipers and measure the cross section of the cord stock and than see if you can get the inside diameter of the ring. Not sure where you are located but McMaster Carr in the States carries a large selection of them and list them by sizes. I do it all the time.
BillWojo