It’s a valid point that Les Misérables is a long book. I’ve got an old copy of Denny’s version and even with small font it gets to 1230 pages, so a lot. I’ve seen a fair number of people commenting that they’d love to write fic, especially about Les Amis, but they understandably don’t want to get the characterization wrong so don’t write anything. Which is a shame.
If it’s just a matter of not having found a copy, the free Gutenberg version is here. (This is for Hapgood’s translation. Everyone seems to have a particular favoured one, and the link here shows a couple in short comparison to give you an idea of which you prefer.)
For the recent 2012 screenplay (without alterations) if you want to refer to it for the film!canon: here. It’s not exactly what comes out in the movie, but most lines have survived the transistions between drafts and run-time cuts.
Les Amis de l’ABC (in order of narrative introduction):
Enjolras, Combeferre, Jean (or Jehan) Prouvaire, Feuilly, Courfeyrac, Bahorel, Lesgle de Meaux (also known as Laigle, or his nickname Bossuet), Joly and Grantaire.
While I would definitely recommend reading the whole book, there is nothing wrong with skipping to the bits you’re interested in, and the chapters are usually only a few pages long. Links are all to the Gutenberg version.
Volume 3: Marius, Book 4
Chapter 1 – Introduction to all of the principle members of the Friends of the ABC, and their meetings at the Café Musain. If you are only going to read any novel characterisation, this is a pretty comprehensive introduction to all of their characteristics and quirks.
Chapter 2 – Marius meets Laigle, a fellow student, who had called the absent Marius present in the roll call at the college to spite one of their professors. He also meets Courfeyrac, who, upon finding out Marius is without lodgings, invites him to live near him at the Hotel de la Porte-Saint-Jacques.
Chapter 3 – Courfeyrac takes Marius to the Café Musain, where he meets the Friends of the ABC.
Chapter 4 – A number of conversations are relayed: Grantaire’s drunken ramblings, Bahorel and Joly discussing their mistresses, Jehan standing up for the value of Greek gods, and Courfeyrac arguing the politics of charters and monarchies.
Chapter 5 – Marius and Enjolras have a political disagreement regarding empire.
Chapter 6 – Marius stops going to the Café Musain. He is having financial difficulties, and Courfeyrac tries to help him get a job as a translator. Through Book 5 (Chapter 1 -2- 3) and Book 6 (Chapter 1 – 6) only Courfeyrac appears, and then, only fleetingly mentioned or else absent.