Here's a Chthonian Dragon retrain custom artwork (thank you @Dokutah Jolly for the suggestion):
https://www.deviantart.com/primeacejohn/art/Chthonian-Doom-Dragon-Custom-Artwork-867136310?ga_submit_new=10%3A1610672698
Free to use for your card-making. All I ask is you give credit when using it.