If your pressure washer is a Karcher then likely you can get a replacement off their website. If you are desperate I think Hozelock do a variety of bib tap adaptors. I got one that fitted a standard bib tap but had an insert that fitted a smaller version, I think they do one that fits a larger size too, certainly I have seen bib taps in garden centres that have a larger than standard threaded end so adaptors must exist.

Richard