I’ve never been able to find it at any of the big fabric chain stores. Instead, you can find it in person at specialty fabric stores that sell a lot of apparel fabric, like if the city has a fabric district. If you’re not lucky enough to live near one of those, then your best bet is to get it online. You can search for alphanumeric pattern paper. Here’s one from Moods: https://www.moodfabrics.com/dotted-pattern-paper-30-yards-11975?utm_source=google_shopping&gclid=EAIaIQobChMI5eOv6sGC1wIVg2x-Ch3TaQcSEAkYASABEgIajvD_BwE