Here is a link you can cut and paste that might help.
It is to "The Collectible Stamp Gallery" even though the initial link says Foreign Christmas Stamps, it still has American US Christmas Stamps.
Just in case the link I am posting does not take you directly to the right section of the website, here is the path I followed to find the US Christmas stamps. It doesn't look like they have them listed in chronological order so you may have to scroll through each page under the US Christmas Stamps section to find the years you are looking for. Anyway, here is the "Path" I took to find the link.
I "Googled" U.S. Christmas stamps 1978 - 1984
Then clicked on
Christmas on Foreign Postage Stamps. Online Sales.
In the left side margin scroll down to the STAMPS section.
Under Christmas, click on United States.
There are several other good websites to check out if you don't find all of the ones you are looking for. They are listed after "Christmas on Foreign Postage Stamps. Online Sales" on the initial Google page where I Googled "U.S. Christmas stamps 1978 - 1984" Here are a few of them.
Here is one from the UK
Also, if you Google the individual years of the specific stamps you are looking for and find what you want. Like "1978 United States Christmas stamp" or something like that.
Hope this all helps. Have fun.