The Postal Commemorative Society's official website is http://www.pcscoins.com/ As a subsidiary of MBI (just as Danbury Mint and Easton Press), information about PCS can also be found at http://www.mbi-inc.com/
There was no Postal Commemorative Society in 1786
250-670 dollars
You can find books on Historic stamps of America 1978 Postal commemorative society on en.allexperts.com/q/Stamps-Philately-1610/2009/2/books-stamps-great-grandfather.htm
this cover bears the 8cent Lyndon b. Johnson stamp of 1973 and the 12cent freedom of conscience stamp of 1980.u.s mint presidential medal 24kt gold electroplated by the postal commemorative society.
You can find 1978 Commemorative stamps of America on about.usps.com/who-we-are/postal-history/stamps-postcards.htm
Coins such as these need to be seen before an estimate of value can be made. I suggest you take them to a coin shop and have them appraised.
You will have to look at an FDC catalog. Not all of them identify the cachet or source of the FDC, but it will give you some idea of the value. And you can always contact the Postal Commemorative Society. Most libraries will have a copy of Scott's Postage Stamp Catalog of the World. First of all, you have to identify the specific stamp or card. That in itself can be a daunting task, but most of the catalogs are well illustrated with lots of information. Once you know what item you have, the catalog will provide a set of prices that can be used to estimate value.
The ones purchased from the US Postal Service include the stamps.
There are a lot of things and offerings which can be found on the Postal News website. However, the Postal News website is focusing on offering hot news.
In 2001, the USPS issued its only Thanksgiving stamp.
It's value depends on what coins are in the 'collection' and the grades (condition) of them. It needs to be seen. Take it to a coin dealer for a value.
Their website is http://www.philpost.gov.ph.