M-Part do one that comes with both crown races:
http://www.sjscycles.co.uk/mart-elite ... prod33893/
I've seen it advertised for less elsewhere:
https://www.google.co.uk/shopping/produ ... CHMQ2SswAQ, but the description at the other sites seems to be wrong; might be worth phoning and confirming that it comes with both crown races.
Or, you could do what I did, bodge it by filing down the crown of the forks so that an ISO headset crown race fits. :?
Also, keep an eye on the stack height. The steerer tube on the forks on my Marin was cut so short that I can only fit the lowest stack height headsets available. Which generally means the cheaper steel ones with caged ball bearings, rather than the nicer alloy ones with sealed cartridge bearings.