I am knew new to model train layouts. Can you suggest source(s) for O Scale train stations to purchase.
Do an Internet search.
Rich
Bachmann offers these in their "Plasticville" line:
Union Station
https://shop.bachmanntrains.com/index.php?main_page=product_info&cPath=267_423_425&products_id=2842&zenid=5ec8pkneao66ntftfdpm2rov42
Loading Platform and Crossing Shanty
https://shop.bachmanntrains.com/index.php?main_page=product_info&cPath=267_423_425&products_id=2843&zenid=5ec8pkneao66ntftfdpm2rov42
As Rich said, an internet search will show stations of various types and sizes available from other manufacturers. Or you could build your own from plans in a book, magazine, or a site such as this:
https://www.scalemodelplans.com/smp/pgs/catalog.html
Len