You can't find it because the combo tickets are no longer offered. Just buy for Acropolis at time you designate... it may b e all to the good, because often you don't get around to seeing all the others, or decide you don't want to. For example, you should check the Kerameikos site... its museum I heard was closed for renovation & don't know if it's reopened. The Temple of Zeus (huge toppled columns) can be seen thru the fence as a walk-by near Hadrian's Arch, ditto for Hadrian's library. The Roman Forum never has impressed me that much; the ONE place I really like is the Ancient Agora, its reconstructed Stoa of Attalos is stunning & a photo op, and full of artifacts excavated when the Agora was uncovered in the 1930s-40s after 2,000 years. however, to maake sense of the ruins you need a guide -- and luckily RS offers you a FREE downloadable audioi guide. Look in LH corner of this page for Watch, read, Listen and click on Greece, then AThens. NOTE: it's good to llisten to it before your trip to get the hang of it.
Also, there are free downloadable audio Guide for the Acropolis, that enables you to go at your OWN time rather thana with a group. He also offers a FREE audio guide to Nat. Arch. Museum - sort of a "top ten" approach, whcih enables you to see highlights & not get lost in long corridors of pots pots pots. The N A M also now offers audio guides, ask for the Classic Highlights one (#8?).