I have an old pair of winter boots that are still in pretty good shape. THe only problem is that the felt inner boots is really worn through in the heel. I'd like to get them back up to speed as an extra pair (got LLb snowclaw pack boots last winter) but I can't find replacement liners anywhere. Does anyone know if they are even available? I'd imagine I can't possibly be the first person who has worn through a set of those liners. All advise is appreciated.