How come there are so many Dragon Slayers? In Fairy Tail, they say that Dragon Slayers are really rare, but it seems like there's more of them than most other kinds of magic. The closest amount of one kind of magic is maker magic; there are 5 people who are shown using it (Lyon, Gray, Ur, Ultear, and Rufus). It's kinda the same thing with Celestial Wizards, they say there aren't many of them but there are 4 in the show (Lucy, Angel, Yukino, and Hisui. There's also Karen who died 3 years ago and I think there's more in the anime during the Clock Arc, but I don't think that is in the manga).

I kind of get why the Celestial Wizards were likely to interact because they were needed for stuff, but if there aren't many Dragon Slayers, wouldn't it make more sense for them to run into more of any other kind of wizard than for 7 Dragon Slayers to just happen to find each other? Other than when they run into Leon, they never meet anyone with the same magic as anyone else in the guild except Celestial Wizards and Dragon Slayers.
There being so many Dragon Slayers despite it being a Lost Magic is an element central to Fairy Tail's plot. Dragon Slayer Magic is extremely rare since the only modern way to learn it is to embed Dragon Lacryma into the body as Laxus, Cobra and God Serena did. Natsu, Wendy, Gajeel, Rogue and Sting are completely different cases as they were taught by dragons themselves more than 400 years in the past and were later send through time to year 777 as part of The 400 Year Plan. Back in the past, Dragon Slaying magic was far more common.