Here's an interesting read for postal history buffs. The demise of a building that once served as a post office in a defunct town once known as Belcoville, NJ during World War I in 1918:
http://www.pressofatlanticcity.com/...b2963f4.htmlApparently the "town" was erected to serve a nearby plant that was producing munitions for the war. After the war ended, the town disappeared as fast as it was built.
The bottom line is that Belcoville, NJ served as a post office for only 9 months in the year 1918. I suspect any postmarks from a post office that was in use for such a short time must be pretty scarce, if any exist at all. In fact, a quick search of the internet, finds no example of a postmark (only want ads seeking them).