Hey I have many things for you!
Eldritch Morgan and he would have been roommates in Slytherin during Hogwarts! Morgan is also a lawyer xD Go figure. Morgan is central-ish in his political beliefs but his family is conservative, so he's very quiet about politics and would be uncomfortable with someone who was not.
Ozymandias Dempsey - if you're involved with Christabel, he's probably her least favorite brother, so there's fun to be had here. Oz is openly disparaging of authors despite being surrounded by them. His political views are "whatever stirs up the most shit" most of the time so I don't imagine they would be friends xD
Tiberius Lestrange and
Victor Daphnel are close-ish to his age and both UCPB. Tiberius is a bigot and would be vocally dismissive of Ambrose's views were they to ever interact, while Victor would be more bemused than anything. He's liberal-ish but 'traditional by default' about any subject he hasn't spent time thinking about, which is many of them. :P
Dorothea Twycross is hurlable, though MC. She thinks he's fun.
@"Juliana Binns" and he could run into each other if he's often found in Wizzhard Books (which her brother owns) or Crowdy Library, as she is frequently in both places. She's very liberal and doesn't mind being outspoken about such things. She's also similarly aged but she was expelled from Hogwarts so they might not have known/remembered each other from school.
Finally,
Thom Pettigrew was the Puddlemere United sponsor before! He is not likely to come back in the near future but if you need some background flavor, Thom is also big in the Quidditch manufacturing industry and would give Puddlemere special deals on team gear and things like that. Unless Ambrose does something to irritate him or makes any negative comments about Thom's (micro)managing of the team, in which case you get no deals forever because Thom can be exceedingly spiteful :P (Also, I'm headcanoning that Thom sold the team in a fit after the Quidditch League bludger changes* and sort of regrets it but won't admit it xD)
*which I realize are not in our timeline because it hasn't been updated in three years, whoops. A bludger hit during the Quidditch World Cup went into the stands and killed someone and then professional Quidditch was paused, then they were allowed to play but with empty stands, then they had to put new protection charms around all the stands in order to get fans back.

MJ made this <3