I had the felt washers made by Ram Gasket Solutions of Redruth, Cornwall (see http://www.ramgaskets.com/washers/felt/). They were the only company I could find who were prepared to custom make a small quantity.
They were quite expensive, costing £72.48 for 10. I still have a few left, so if you are interested in purchasing some, send me a private message. Alternatively, if you want to try and get some made yourself, the dimensions of the washers I had made were 133mm outside diameter, 112mm inside diameter and a thickness of 12mm.
Hope this helps,
Sean