Hi girlie... you do not need an invite for a trunk show but in order to know that one is going on, you would have to receive one in the mail. If you have purchased in the Chanel boutique before I think they automatically send you an invite, but if you don't have one you can show up anyway and no one will kick you out, its not exclusive...... and yes, they do take names for the bag(s) you want. Usually they have samples of upcoming bags out for customers to see. But Swanky's advice about striking up a rapport with the SA where you shop (and where the trunk show will probably be) is a great one. SA wll notify you of upcoming shows.
there may be a Chanel trunk show near you coming soon, as this week on Thurs and Fri, Chanel is having a trunk show in Town Center Mall in Boca Raton where i live, from 10 til 5.* .
* i just may camp out at 5am, waiting for store to open, like a teenager in line for concert tickets LOL