There is an Anglo-American team in America that comissioned a mill to make them period weight Kersey and from what I hear they are doing a bang up just in selling it, infact having a hard time of keeping up with the runs, which is surprising considering I can not find these guys! None the less most of the larger re-enacting supplie shops carry their line.
So far as I know, there is no "period weight kersey" available in the US that compares favorably with the real stuff. Several suppliers offer a heavy weight, heavily napped woolen but there is no "kersey weave" visible if you scrape the nap off. I'd appreciate more information if available.