Ha, good luck! I once saw a bottle of Pappy 23 Year at Liquor World in Porter Square (last year). I've never seen any other of the Van Winkle varieties anywhere, not even the Old Rip Van Winkle Handmade Bourbon--nothing. I tried tracking down the Buffalo Trace Specials at Downtown Wine and Spirits and they didn't have anything. They had me write them and I never heard back. So maybe you will have better luck than I did.
Not to be discouraging, but it would be a minor miracle for you to find it. As you probably know, most liquor stores have very small allotments, and they either save what they get for preferred customers of employees. Many places keep wait/request lists much longer than any inventory they could expect to have. I have heard of people stumbling upon random finds of Pappy at the NH state liquor stores. It is an excellent product which got hyped up in the WSJ among other places. Now you have the increased pressure of people seeking it out as a status symbol. Good luck.
Try Federal Wine and Spirits. If anyone has it, they might. We were able to get some 20 yo pappy there a couple of yeas ago. Marty's also has a fairly deep bourbon selection.
675 Washington St, Newton, MA 02458
Federal Wine & Spirits
29 State St, Boston, MA