Buffy continued with season 8 in the comics (They are considered canon). It's currently on season 10 which they 発言しました would be the last season. I'd try www.tfaw.com or amazon.com
The 前 poster's suggestion for tfaw.com is a good one. I've bought many comics from there. Another good option is Comixology.com if you'd prefer to buy digital versions rather than paper copies. It's a bit cheaper that way.