Strack's three volumes are not available online, so the only source is the second-hand market.
The
Trajan and
Hadrian volumes turn up somewhat frequently, because
Peus c. 1970 purchased a supply of these that
had turned up somewhere and retailed them very reasonably, like c. $20-25
per volume.
Antoninus Pius, however, was not included in Peus' stash, so that volume is much harder to come by.
A fourth volume,
Marcus and
Commodus,
had reached the stage of page proofs before WWII destroyed it:
Strack was killed in the war and the publishing house in Stuttgart was destroyed by Allied bombs!
