The US Mint struck the 1936 York County, ME Tercentenary Half Dollar in August 1936; it produced a total of 25,000 (plus 15 assay coins). The York County Tercentenary Commemorative Coin Commission ("Commission") indicated that of the 25,000 coins available, 10,000 (i.e., 40%) were to be reserved for residents of York County and the State of Maine.
With coins in hand in late August 1936, the Commission began local advertising to promote the coin's availability; advertisements were placed within and outside York County. Those interested were directed to banks in York County and the Portland National Bank in Portland. (Portland, Maine is within Cumberland County vs. York County.)
Advertisement Run in the Sanford Tribune and Advocate (Biddeford, ME)
Advertisement Run in the Portland Press Herald (Portland, ME)
Though sales began strongly, they soon slowed. Approximately 6,000 coins remained unsold at the time the Commission wrapped up its Tercentenary duties. The unsold coins were
not returned to the Mint to be melted, however. The remainder coins were held and periodically sold in group lots at discounted prices; coins were available into the 1950s.
Interestingly, the Commission made public statements at the time of the coin's release that indicated that the 10,000 half dollars reserved for Maine residents were not enough to fill the orders received. The filling of in-State requests were made a priority, and coins from the out-of-State supply were reallocated to fill the local orders. Considering that roughly 6,000 Maine half dollars remained unsold at the close of the original sales period, questions could be raised regarding whether the local-order announcement was fabricated to hype sales and drive new orders, or was a case of factual reporting. It doesn't matter much, IMO, as all 25,000 coins that were struck eventually made it into the marketplace and nice examples of the York County, ME coin are not that difficult to encounter.
1936 York County, ME Tercentenary Half Dollar

For more of my topics on commemorative coins and medals, including more on the history and design of the York County, ME half dollar referenced here, see:
Commems Collection.