Various ticket buying services are listing Twilight tickets. You are able to buy for the opening weekend and beyond depending on the theater and the location. Do check back if there is a location that you are interested in that doesn’t have a show time you want yet, especially a midnight showing. Sometimes those end up getting listed later on.
Your best bet is to see which service works is your area, some are merely mentioning that Twilight is upcoming vs. others will let you order.
Fandango has a couple of clips up. The second one down has a few brief seconds of the Port Angles clip mixed in with previously seen footage. TY to Jenny for the heads up.