Reddit mentions of To Rejuvenate and Nourish: Nine Days of Prayer to Asklepios, God of Healing

Here's a small devotional book for him. There's also a few decent scholarly books, most notably Asklepios: Archetypal Image of the Physician's Existence by Carl Kerenyi. And an interesting book by a therapist about using the dream incubation techniques of Asklepios' ancient sanctuaries in modern healing work.

I'm afraid there probably aren't many modern polytheists devoted to him particularly, so you're going to have to go back to the source material and build cultus from there. But, we have a lot of source material!