: 1) how would the baron have found it?
: 2) why would he want it?
I reckon Soulblighter recovered it from the area. Think about it, the explosion at the Devoid may have uncovered some juicy stuff, so after the dust settled, he probably scoured the area for goodies. He probably found the Journal and read it to learn more of the tactics of the West and maybe find out any info Alric knew but Balor hadn't told him. Also he would have found out about "a man not yet born, who would ressurect the Myrkridia".
So, back to the question. The baron's flavour text is as follows:
"The Baron came to power ten years ago, appearing out of nowhere. With the aid of his brigand cohorts, he laid claim to Keep Kildaer and the surrounding lands. "
So I assume hat he was in the Untamed Lands when Soulblighter fled there. He was probably one of his disciples and when SB thought he was ready, he told him to set up camp in Forest Heart.
"Stygian Knights are a rare sight as they are created only by Soulblighter and given as guards to his human associates."
"As Soulblighter's corrupting influence spread, many weak and unsavory soldiers were swayed to his banner with false promises."
Just more text to back up his allegiance with SB. When SB finished witht he Journal, he gave it to the Baron who could safe guard it in his keep while Soulblighter began his military campaign against the Light.
