As a rule, it's perfectly acceptable to have two "that's" together. However, you are one of many who try to avoid it for stylistic reasons, which is also OK - so long as you do not confuse the meaning. Thus, you could not simply drop one of the "that's", but you could substitute "this year" if the event had not yet occurred. Otherwise, I would express it as "... announced that that year's Regional Band...".
I agree with you about the comma.