1. Get a ruined rim from a junkyard and then have someone with a good hydraulic press and considerable skill press them out of the junk rim and into your good one.
2. I have seen them on the websites of some of those companies which advertise custom lug nuts and bolts and spacers, etc., etc. Do a search with "lug bolts." I'm sorry, but I don't have time to search it out for you right now.
3. Look in _Autoweek_ or _Road and Track_ for ads from places which repair expensive rims; call and see if they can supply you with what you need, either new or used.