Metro creates PDFs for their flyers but they’re not posted on their web site. An e-mail to Metro’s customer service will get them individually so I made a public records request for all available PDFs available for Metro-operated routes. My request only asked for routes 1 through 373, excluding any custom bus, school bus, or DART routes, but Metro also provided the Group Health and DART routes. The Spring 2015 schedule flyers are now posted here. The flyers were given to me in five larger files so I split them up into individual ones for easier downloading. There is one page missing, for the 150/164/168/169 combo flyer, and I’ve asked for it to be resent. A single file of all routes provided to me is available [PDF], as are the five files sent to me by Metro. If a route is combined on the schedule flyer, like routes 2 and 13, or 31 and 32, there is only one file for them and it is named after the combination (for example, “Routes 2 and 13.pdf”).
As part of the request, I asked if Metro could post these files on their own web site but that answer is still pending.
In addition, since the latest Sound Transit PDF book I can find is June/September, 2013 [PDF], I’ve put in a request to Sound Transit for their latest version if one is available. Update: Sound Transit got back to me and pointed out that their Ride the Wave PDF is in an obvious spot, on the right-hand column of the Schedules page. Once there, the latest book [PDF] can be found.