It seems like most “slaves” in the galaxy have implants that slave-owners can detonate if they try to escape. Anakin and Shmi mention having them in TPM
We really see slavery only once in the saga, which is in TPM, and there, slaves have bombs in them. Concluding that most slaves all over the galaxy also have bombs in them seems like a bit of a stretch. Especially since TFA takes place 60 years after TPM.
It’s given a passing mention in AOTC as Anakin goes to see Watto, who has long since sold her to Cliegg Lars, who freed her.
Whether anyone besides Oola, (and her royal replacement) in Jabba’s palace is a slave is up for debate.