Indiana's ASA 2-day school is among the best clinics I've been too, regardless of organization. Indiana is blessed with some of the best ASA umpires, hell, umpires period, in the nation. The two-day school is usually in the last half of march. Also, ASA offers two hour clinics (new rules) and 8 hour clinics, as well as one-day youth schools for umpires under the age of 18. A great training regiment.
Keep visiting
www.inasablue.org and you'll find information when it is updated.