Some ideas:
1) Rather than an auction, simply take out an ad in relevant magazines like the duPont Registry, Robb Report and RR's special motorcycle edition that comes out every couple of months.
2) With that high line of bike, you might consider going to a high line auction house that handles motorcycles. Get a copy of dPR and RR and you'll find most of the reputable ones advertising there.
3) Call around some of the bigger custom houses and ask for a referral on a consignment sale.
4) List it on eBay and look to put out the information on relevant discussion sites. And/or create a profile for the bike at Link hidden: Login to view and use the url to promote the auction.
Some of these forums have buy & sell sections, as well as discussion sections of premium and collectible bikes:
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Good luck with the sale! Once you have some pics up I'd love to see it -- unfortunately not in the market for any $100k+ collectible bikes myself, but I am an enthusiast.
Frank