The Index, sure. That was never published digitally. The hardcover can be bought but regularly goes for well over $1.500. The others are available from various stores:
https://www.amazon.com/Tihkal-Continuation-Alexander-Shulgin/dp/0963009699
https://www.amazon.com/Pihkal-Chemical-Story-Alexander-Shulgin/dp/0963009605
Might I suggest the second half of TIHKAL.
Also, r/PsychLaboratory right down the hall.
Also the second book Tihkal if you’re more interested in tryptamines as Pihkal is about phenethylamines
I got mine off Amazon. https://www.amazon.com/dp/0963009699/ref=cm_sw_r_apa_i_aMVGEb7XG89WN