A while back I was able to find pricing on a separate 7 day travelcard for the metro. I can no longer find that option on the tfl website. I only see an option to combine an oyster card with a travelcard. Is the 7 day travelcard no longer available?
The paper travel cards can be purchased at National Rail stations rather than tube stations and used for the 2-for-1 entry discounts at many places. TfL still sells some paper travel cards (daily ones at least and I think others), but most people who do not want to access the 2-4-1 deals and who need more than a 1 day card, find it simpler to load it onto an Oyster, along with some pay-as-you-go (paygo) money to cover anything the travel card doesn't. The Oyster will calulate the best deal for you and deduct accordingly. Any unused paygo money and the deposit you paid for the card can be refunded prior to leaving London if you wish.