If you are able to locate a PO that actually has this particular stamp sheet, it's really a function of whether the clerk is willing to break up a whole sheet just to give you the one stamp. Results will vary by location. Perhaps you'll encounter an office where they already broke a sheet for someone else, and would thus have no problem selling you just the Mount Washington stamp. But, if you'd like to buy large numbers of just this stamp for your postage purchases, you'd probably either have to buy that many full sheets, or simply pool your resources with others so that collectively you purchase the desired number of sheets, without any particular person being stuck with a large number of stamps they don't want.