Tracing Genres through Organizations (MIT Press, 2003) is no longer available in hardcover—it's out of print. However, it's still available in the Kindle version. And if you want it in paperback, it's now available, both at Amazon and at the MIT Press site.
Network (Cambridge University Press, 2008) is available from Amazon in all three formats. I'm very excited that it's now available in paperback, which is much less expensive than hardback.
I haven't seen the paperback version of either book yet. If you buy one of these in paperback, let me know what you think!