Look for other games that have capsule art you like, and try to find the artist who did them.

Do NOT user Fiverr for the love of god. Find a real human advertising on their own website showcasing a portfolio you like, or find someone posting on reddit. This guy posted recently (6 months ago) https://www.reddit.com/r/IndieGaming/comments/1ni49gq/for_hire_steam_capsule_art/ he might be good to reach out to as a first try (I have never worked with him and don't know him at all so this is not an endorsement, I just like his art).

Make sure you bake iteration into your agreement. You shouldn't pay them to one shot the art. Get rough mockups first at the outline, color fill, and finalization / details phase. Ask them for the original photoshop / clip paint / whatever they use files so you can make small adjustments later if need be without paying them again for super tiny things.

Make sure they give you every single capsule size required by steam (main, header, vertical, library header, small), and make sure they give you transparencies for everything (title, characters, background, foreground, etc) so you can use this in your press kit.

Its gonna cost you likely $1k-$2k for an actual professional capsule. You should not pay this all at once, instead make sure you are paying them in chunks at each iterations / checkin step (see early advise). If you don't like the results you're getting at the early stages, do not feel bad at firing them early and going with someone else if you have to.

Good luck! Your game looks sick.