I done some looking and found alot of folks asking for tappered shaft adapters, found talk of some out there, but found no resources. So I went to ebay. They have alot of tappered adapters for drill presses so maybe you can find what you need that way. Or machine a tapered flywheel or clutch down and cut a key
http://www.ebay.com/itm/WARNER-SWASE...#ht_500wt_1054
http://www.ebay.com/itm/5C-Collet-Sp...ht_2777wt_1037
http://www.ebay.com/itm/Oneway-Taper...#ht_760wt_1270
http://www.ebay.com/itm/Air-Filter-A...ht_1073wt_1037
I've also read of folks starting the engine and turning the shaft down with a grinder or what not, having a shop turn it, or new crank. Hope one of them at least gives you an idea