try a google search for mod trials stems. They're not on most bike parts websites so you have to do some digging, but they come in some nutso sizes like 165mmx35d, 180mmx40d.

examples:

http://midwestbiketrials.com/store/i...products_id=10

http://cgi.ebay.co.uk/onza-black-all...e#ht_600wt_941