In order to get QR Codes, talk to Sable 10 days straight. Then a weird sewing machine comes. The sisters do not know how to use it, but you can use it! Go online and find some QR codes to scan. Just talk to Sable, say yes, then put your 3DS camera over the QR Code and you have a pattern!
Good places to find QR codes[]
here are some nice QR code sites: