Before the attorney, I would:
--try to get the principal on the phone (some people just don't do email well), noting time and date of the phone call attempt in your communication log (you have one, yes? if not, start documenting everything in writing, in ink, with dates)
--if that doesn't work, send a paper letter that outlines the needs and asks him to respond by such-and-such a date. Copy the person in charge of special ed in the district and/or the superintendent, and put the CC line at the bottom of the letter so the principal knows they've been copied.
--then, yes, outside help. Do realize that once YOU have an attorney THEY will start bringing one to meetings, too, and it can become more confrontational on the whole. You may want to go to an educational advocate instead as first line of defense.
Sorry about the NP. Hang in there and persist. I think it will be worth the trouble in the end.