Ishmael, obviously... he thinks he's slightly suspect for going to the Ministry but would still begrudgingly lend a hand if Dimitri ever needed it.

Once again my Dempseys were in Ravenclaw at around about the same time (...Phyri is more interested in books and, as a weirdo, has no qualms about hanging out with vampires lol).

Jude was also in his schoolyear if he's interested in talking rights for non-humans.

Jay was in the year above but same house and also a scholarly type in his Hogwarts time, he is a night owl so could be a low-key friend for Dimitri in this day and age!