How to find wallpaper matching existing wallpaper?

Well, it's a red toile pattern ... depending on how big the spots are though, I'd probably glue some sort of base material into the tear, smooth all the edges and then go at it all trompe-l'oeil-y style with acrylic paints to "match" (both background color and pattern). And then I might paint in a three-headed dog or godzilla vs mechagodzilla into the landscape, but that's just me. If you aren't handy with painting like that, maybe one of your friends?

If you want this to look nice and seamless it might be worth hiring someone experienced in the fine art of wallpaper hanging to patch it up. They might also know a secret spot on the wallpaper that reveals the brand and style number that they could delicately dislodge or something. I've never dealt with wallpaper myself, but my parents used to have a lot of it in the house and the wallpaper hanger dude they used had a whole bag of tricks (or maybe just fuckloads of patience?) for making the paper look good in uneven/difficult/torn spots. I do like Rube's godzilla idea though.