I don't remember all the salts but:
Just check the more obscure places you never go.
Edit:
That giant slug is interesting. It's theorically killable with evasion+pursuit. If you manage to get it's 999 negate damages down, you can damage it normaly with pursuit damages. It will takes hours (way more than randomly finding all the salts) for no benefits but it's doable.
Black Locust Bride and a full team of Pursuit FM should speed up a tiny bit the process.
The slug is supposed to have 999 guts too but I guess it loose it when you got the 5 salts.
With that really long test for nothing (I got down that 999 negate damages...), I can confirm that unless all the other damages in the game, Pursuit is fix and not affected by defense. The only kind of boss able to reduce pursuit damages is the secret garden bosses and takes 1 damage from every damage source. I guess theuir damage reduction is hard coded and don't rely on defense or any other damage reduction mecanism.
I think we could use that giant slug and evade team to calculate the internal turn limit (assuming it's the same for every type of stages. It seems it's lower in the castle). But I'm not sure I want to stay for 1+ hour with a paper and count every single turn...