There is no "proper" article to use before "old DVDs" because the phrase describes a general category of items in the plural form. Why No Article?
If you are looking for places to shop, enthusiasts on Reddit and resale experts suggest: where to buy old dvds
If you tell me , I can find specific local shops near you. There is no "proper" article to use before
: eBay and Amazon (used section) are the largest sources for rare or out-of-print titles. where to buy old dvds