Please leave an "Item Wanted" message in the appropriate category.
Your email address is not necessary - a potential seller can send you a message right from your listing.
To save unnecessary corespondence, you should leave a price you are willing to pay.
Please check the appropriate categories occasionally - you may just find a sale waiting to happen!
If an item wanted price is close to your selling price, or even if you have an item similar to the one the buyer wants, you may want to try negotiating.