There is the possibility that a seller may sell the wheels separately, but chances are they would charge a premium. The worst thing that could happen is the seller says no. But if it's getting this hard to find the OEM custom wheels now, imagine what's it going to be like in five to ten years.
I do believe Craigslist allows WTB postings, so I'd post an ad and keep reposting until I found something. Though I'm thinking ads like that may be an invitation to be taken of price wise, but if you set a budget of 5-8 hundred bucks that should help weed out any price gougers. But I'd also post wanted ads on all the Kappa forums and keep bumping them up because I think we're the best resource for finding and helping each other find Kappa parts.