Ready + Reaction + damage# = kills the conc side of the spell, I don't think it stops the spell altogether.
... a build that focuses on triggering exactly this, isn't necessarily bad at all the rest of combat = might be interesting.
Moving within 5' range (+probably Reaction +maybe a ready too) = forces disadvantage on most spell attack rolls, smaller subset than conc spells, but lots of cantrips.
... weird build, to just chase the spellcaster, while archer-ing the rest of the encounter dead, then
finish the spellcaster. No one's done this, but it would work. Could be a grappler that doesn't bother with the grappled.
giantitp had an extended thread quite recently, but I haven't read the whole thing yet. (and who has the time really?)http://www.giantitp.com/forums/showthread.php?583570-What-ways-are-there-to-disrupt-spellcasting-in-5e
I'd love to see a mini-guide or summary on this exact topic.
edit --- Misterwhisper starts a list of spells that get by Mage Slayer (not vetted).http://www.giantitp.com/forums/showsinglepost.php?p=23789395&postcount=245