Since we don't have access to a milling machine, I've been trying to find a source of reasonably priced aluminum sprockets. This may be a good source
http://www.jackssmallengines.com/gok...msprkt_35f.cfm
19 to 94 teeth, prices from $14 to $36. Looks like they will custom drill them, though they don't list the cost for that.
Now all I need is a reasonably light flange with a keyway to attach them to a 1/2" or 5/8" shaft.