For pres dollars you should be able to find a bank that has a few. Usually they will order a box when they first come out so if you start visiting everyday on release date for about a week you'll probably get first dibs. Other ideas find a nice teller. When you are in the bank on other visits such as depositing your paycheck. (Usually when your handing them money they're in a better mood.) Ask the manager to order you a box on next weeks order. Now this would require a lot of upfront money but you can take the ones you want.
Then you can go to another bank and return the ones you don't won't. (Don't hand the teller that ordered them for you back half or more of the box. They may be angry and not do it for you again) Or you could see if a local dealer wanted the extras at face. (Never could hurt to be on their good side.) Once you get 50 posts you could sell/trade them on here.
Best part in this there is no premium like
ebay or a dealer. Good Luck.