Hello and welcome!
I can direct you to a BUNCH of public domain stories in the MMC Christmas Library. I've sent you a PM (personal message) with more information.
For other good sources of public domain Christmas literature, go to Project Gutenberg
. Also check out Librivox.org
, which has hundreds of free-to-download audiobooks of public domain literature, produced by dedicated volunteers. (I know they'd love to have you as a volunteer reader, with your interest in public domain literature!) Each audiobook entry in their catalog includes a link to the material from which it is read. All these sources are searchable.
You might also go to Google Books and search for digital copies of the old Saint Nicholas Magazine for children. I've found numerous public-domain Christmas stories there.