I have been satisfied with purchases from Elite Obsolete Electronics. YMMV, of course. iFixit and iDemiGods also sell parts, and there are numerous things for sale on eBay. You will need at least one opening tool. I suggest watching a few YouTube videos on the subject. I've never opened a 7th gen classic, but it has the reputation of being difficult. So, when you have the old back off you might want to consider replacing the battery.