Definitely! You can get the Museum Pass for 85TL (Summer 2014 price). It will be valid for 72 hours starting from the first visit to any museum that accepts Museum Pass. Here is a list of museums that accept Museum Pass and their actual ticket prices:
Chora museum (15TL), Hagia Sophia Museum (30TL), Istanbul Archeological Museum (15TL), Istanbul Mosaic Museum(10TL), Topkapi Palace (30TL), Topkapi Palace Museum Harem Section (15TL), Museum of Turkish and Islamic Arts (20TL).
Also, there are discounts at stores, and some private museums for the card owners.
You can buy the museum pass online and have it shipped to your Istanbul address, however, I don't think it will be wise to wait for the delivery guy to bring your card to you.
You can also buy from the mobile sales points, which are minivans parked at museum areas.
Probably the best bet would be going to one of the sales points at the museum entrance of Topkapi Palace, Chora Museum, Istanbul Archeological Museum, or Hagia Sophia museum, and be done with it. I think the least crowded museum would be Istanbul Archeological Museum.
Here are the number of visitors of each museum in 2011:
Hagia Sophia: ~3.200.000
Topkapi Museum: ~3.025.000
Chora Museum(Kariye): ~387.000
Istanbul Archeological Museum: ~382.000
