There are several Sonic Skins you can download here: https://drive.google.com/drive/folders/1DdPxbCkdaK2pPv-GA9YRKXQRk_Lv_gky
I strongly recommend the Legacy_Sonic3_Reskin.zip that "the_swordsman_ps4" (on Discord) and I made together. It's basically a Sonic 3 inspired set of sprites for Sonic. They were used in previous versions in the game, but a few months ago were updated to the most current version. (Actually, I still need to fix his Controls Sheet... I need to get back to that).