The Bow skill should be available at Knights Blade on Emerald Isle, and also at Tempered Steel in Harmondale Village just about due east of the Castle. If your game doesn't offer it to your cleric, I'm baffled.
In particular, if you take the Light Path, the assault on the Hall of the Pit with a Light Path party is, I reckon, one of the best battles in the whole of the Might and Magic canon.