Regarding elementary art curriculum sources: I usually write original
lessons. I have an extensive art library built up from years as a
commercial artist, plus have bought many books that interest me
(subjects like altered books, clay techniques, watercolor techniques,
just anything that I would like), then I work backwards, chunking the
steps, making things accessible for my upper elementary students.
Sometimes a new artist or children's book inspires a project. Starting
with a "big idea" (e.g. "how do artists use line?") or "essential
concept" (e.g. "texture") is helpful, and of course, your benchmarks.
ASCD publishes several good titles regarding writing curriculum. I
curriculum map my entire year first, which is helpful. I have not
found good elementary art curriculum books, I think they are too
"crafty" or simplistic, generally. Also, students love technology, so
we've been doing Photoshop, webquests, Smartboard, advertising, and
anime. I'm thinking of adding the "rotoball" project (can check out at
Art Ed 2.O).