Is the "Summer in Centropolis: The Official Companion" book in the Summer in Centropolis bag?

If not, how/where do I get it?

Nope. I think it's a contest prize from awhile back?

I'd guess it'll be in the crystal shop or something one day.

Aw, damn. Thanks.

Indeed, was a prize for the original competition. SubetaWiki has the breakdown (not vouching for accuracy but it seems right) towards the bottom of this page.

While I would normally say Crystal Shop as well, I could see them adding the book to the bag - similar to how one of the 100k/celebration minions got added to that bag... except that the entire bag there was already in the crystal shop. So /shrug? Obviously no one is sure, but even more not sure c: