where do you get those markers??
I’m assuming you mean physical markers, since this ask came around when I posted that Alexandrite drawing, iirc.
I really got them from a bunch of places? Markers can get really expensive, so I’ve collected them over the years. Copics’ll cost you the most; there’s this misconception I see here and there that Copics are completely superior because they have a brush tip and you shouldn’t use Prismacolors because they don’t (though I think they do make a limited selection of Prismacolors that do have a brush tip, now? But that’s besides the point), but I’ve found that they both work perfectly well together! And Prismacolors are cheaper, too. I would shop around for prices before picking anything up, and buy markers (especially Copics) when they’re on sale!
EDIT: As for the actual “where,” most art supply/hobby stores will sell one or the other, if not both. If you have a local art supply store, I’d give them a shot! If not, Michaels sells them, though their prices aren’t the best.