There are thousands of picture books published each year. There are many places to find lists, but here are a few. The Children's Book Council has a "hot off the press" feature on their site that lists new books by publishers who are members. While not all publishers are members, many are (you can find a list of members on the site as well).
You can also look at fall and spring announcements from Publishers Weekly.
The American Library Association lists the year's award winning and notable books.
There's also the New York Times Review of Books.
Also, ask a children's librarian! Our library's website has a monthly feature that lists new arrivals in the picture book area.
Your local independent bookstore is another good source. They probably carry the free Indie Bound newsletter "Kids Next," which has recommendations from booksellers across the country.