If you are in or near Connecticut, check out Sail the Sounds for a two-day ashore, one-day aboard Celestial Navigation course. My son got certified in Coastal Nav from here, and they're awesome!
Starpath has a terrific home study course, which I highly recommend (I took it myself). You get email and phone help from an extremely helpful staff. PLUS THEY HAVE A NEW ONLINE COURSE!
Sail Due South (cc), is a South African sail training school with its main base in Langebaan on the West Coast, and a satellite school at the Vaal Dam. The Yachmaster Ocean course under Advanced Courses has celestial navigation.
Ocean Classroom Foundation runs educational programs from its schooners Harvey Gamage, Westward, and Spirit of Massachusetts. Its Navigation/ Seamanship course description states: "Navigation studies begin with basic chart plotting and progress to celestial navigation. Students gradually learn to determine the ship's position using the sun, stars, planets and the tools sailors used prior to the age of electronics."'
Liveaboard courses on the Saman, a 52-foot ketch, in the Gulf of Maine and the Caribbean. I haven't been on one but they have received rave reviews --- I'd love to go!
The Planetarium at Mystic Seaport in Connecticut has on-site courses as well as one-day sun shooting classes. They also sell a great book----Susan Howell's (see my Practice page), which you can work through yourself at home.
Disclaimer: I get no money or anything else from these schools – I list them because I like them, and I’m the boss of my webpage!