I had purchased USPS mail use packs for 2014 and 2015. It did not have all the stamps but got me going. I have found Fort Pitt Philatelisc eBay
lots not too unreasonable but usually complete for commemoratives.
For 2016, I have all the sheets (annual Christmas gift) and purchased more from USPS to get singles. My order in late December has not arrived yet with some booklets and have plenty of extras now. I have strips of 1c,5c,10c coils along with others that USPS sold as blocks of 4.