Sounds like you're referring to Luggage Tags? You can purchase them at the boutiques (and probably via the 1-866 number) and yes they are hot stampable. I don't recall how much people said they cost (I want to say slightly less than $100) but if you do a search in this forum for "Luggage Tag", you'll probably come across a reveal or two where the price is mentioned. Good luck.
Yep, you sure can purchase them separately. There are two sizes. I'm not sure how much the little one costs, but I recently (after the last price increase, I believe) purchased the larger one in the chocolate brown leather (the one that goes with Damier Ebene) and it was £33 (about US$51). I just called my nearest store and had them hot stamp it for me and mail it to me. You can't buy them online but I believe you should be able to order them over the telephone and if not, they'll connect you to a store that has them in stock and they'll do a charge-send.
I called the 800 number and they found a boutique for me that had them in stock. I spoke with them on the phone, told them what size and what color to heatstamp, and of course my initials. To order 2 of the small damier ebene with shipping from Florida to Atlanta was $129. For some reason the vachetta cost me less ~ $35 for the small ones and $51 or $55 for the larger. They seem to always be out of stock at my local Atlanta LV, so I always order with whatever boutique has them in stock around the country now. Hope this helps.