James - Do you still have an interest in trading rocks? I would be interested in a sample of your Kentucky kimberlite.
I have rocks from north shore of Lake Superior as well as other rarer rocks.
Please contact me via : email@example.com
Hello James, as it happens I have several specimens of serpentine (I live on the Lizard peninsula) that are surplus, some even cluttering up my doorstep! If you are still interested then please do get in touch. If I dont have what you require I could always take a trip to Mullion, Gunwalloe etc and collect you some.
I also have several specimens of chalcopyrite from St. Hilary (near Penzance) that are going spare.
You say you are looking for "nice hand samples", nice being very subjective but I see all serpentine as being 'nice', chalcopyrite too!
This is of course if you live in the UK...I assume postage overseas of rock samples would be horrendous.