I don’t know if you can get specific profile comments, because I can’t find anything about it.

Yes, if you can get projects and users, comments work.

…Huh. I thought that this would be pretty straightforward, but it looks like this might actually not be possible…
That's a shame if so. I sometimes use the studio APIs to be able to view early comments in popular studios without scrolling so much my browser gets hung up; it would be nice to be able to do the same for user pages!
We might just have to wait until user pages get migrated to Scratch-WWW, I suppose.