I was sure that I would be able to give some background information on Jim Hart, but I have found very little from the usual sources.
However, Jim is an American artist, producing mainly millefiori weights in concentric designs. As well as regular style millefiori canes, he makes silhouette and rose canes. I think he has been making weights for over 12 years.
He sells his work through ebay and etsy.
His ebay name is jhpaperweights and
This Link shows, via eBay UK, some of his latest completed items.
Perhaps direct contact through the eBay system will be the best action.