It's been over a month since The Book of Mormon went on sale in Los Angeles at the Pantages Theatre and most of the shows are sold out or nearly sold out. If you're looking for a weekend show, there's only a few sparsely placed single orchestra seats and a couple seats in the very top and back of the theatre. It's safe to say, it's too late to get any good seats through the box office; but you can still get them through the secondary market for a premium.
Because of the high demand and somewhat short run in San Francisco, SHN (Shorenstein Hays Nederlander) theatre in SF has decided to make The Book of Mormon, along with a few other shows, subscription only. What's that mean to the average theatre goer? You have buy the entire season of shows just to get a ticket to BoM! As of now, that's the only way and SHN expects to sell out without releasing any to the public through a public on sale. That said, if their expectations fall short, I would expect that they will be having a limited public on sale in the middle-end of August. For San Francisco, if you're not a season ticket holder, your best bet is the secondary market. Expect that market rate for tickets will be upwards of 2-3x face value. SHN season tickets include the following shows in addition to The Book of Mormon: Diner The Musical, The Lion King, Anything Goes, and Wicked. Diner, Anything Goes, Wicked and The Book of Mormon are available through season subscriptions only; while The Lion King, and War Horse are available as single show tickets.
Seattle seems to be following suit with San Francisco. As of now you cannot purchase tickets specifically for The Book of Mormon at the Paramount Theatre in Seattle. Only through a season subscription that includes the following shows: War Horse, Fela!, Flashdance, Sister Act, and the option to additionally purchase Wicked tickets. If you're not up to spending hundreds or even thousands of dollars on a season subscription to see The Book of Mormon or any of the other menitoned shows, you should check out what's available on the secondary market... you'll pay a premium, but you wont have to buy an entire season of shows when you only want to see one or two. In the end, it's less expensive.
Below are some links to what's available, keep in mind, these prices are the actual ticket price... no fees, no shipping; just the price of the ticket:
The Book of Mormon: