There's a lot in The Starseed Signals about Timothy Leary's book Terra II. As far as I can tell, though, the Timothy Leary estate has allowed Terra II to go out of print. (The bibliography of Timothy Leary's books on Wikipedia does not list Terra II but lists something called StarSeed, which I'm thinking must be the same work. Then again, the "His Works" at timothyleary.info list the titles separately. So I don't know. )
If you are curious about Terra II, I wanted to point it is available for download at the Internet Archive, in a variety of formats.
To reiterate my position on copyright, I am generally rather conservative about the issue: If something is commercially available, I don't think it should be posted. But if this is the only way to obtain Terra II (or anything else of scholarly or artistic interest) it seems to me making it available is a public service. It's possible someone might disagree with me, so it might be a good idea to go ahead and download and secure a copy of Terra II, just in case.
I also want to take a moment to note that quite a few works by or about Timothy Leary are available at Hoopla Digital, the digital library service offered by most public libraries.