While cards made from blank cards won’t be legal for tournament play, there are still plenty of uses for them and several online retailers you can buy them from. Of course, you can also make your own!
Magic the Gathering: Arena, Page 121
The 3 Best Places to Get Blank MTG Cards Plus How to Make Your Own
The 46 Best Discard Cards and Effects in Magic - Draftsim
The Top 6 Proxy Websites for Magic - Draftsim
The 46 Best Discard Cards and Effects in Magic - Draftsim
Reviewed: The Best Custom MTG Card Sites & Apps - Draftsim
free card maker — MTG Forum
The Top 6 Proxy Websites for Magic - Draftsim
Zendikar Rising Draft Guide - Card Kingdom Blog