As an ebay buyer, I have been contacted by the seller ("I have another one if you're interested")
and by third parties ("I see you bid, but didn't win...I have one to sell").

I accepted one of those offers one time (from the seller), and I got burned. I now "just say no" unless it's someone I've dealt with before.

As to the original question, I don't think it's right to contact someone, unless it was your auction. The original seller is the one who has done the work and paid the fees to get the contacts, he should be able to reap the rewards if he has duplicates. If you want the contacts, you put the item on ebay. Just my opinion!