I'm no help myself but I searched here on itch:
https://itch.io/game-assets/tag-mega-man
And I found this one:
https://untiedgames.itch.io/mechanical-fortress-tileset
Maybe reach out to the creator and consider joining his patreon. He has a fitting style and it could be way cheaper to buy some of his assets isntead of paying someone to just draw for you.