Need help with Geralf

https://archidekt.com/decks/16349567/geralf

So I made this deck except I overlooked the fact that I can only have cards in my deck that have the color identity of my commander. Geralf is blue only. So you can see my problem. I built a zombie deck (bought all the cards already) but obviously this isn’t legal cause I wasn’t paying attention (I’m new to magic). The deck basically revolves around zombies and my hope with Geralf was to make it tribal zombie. My question is, is there a black and blue legendary creature that will still work with my already built deck or am i just gonna have to start from square one again? Thanks.