Assuming your standard is high(?), I think it is very unlikely that you will get an exceptionally done cover for free (the sort of standard you see from creators with many followers or very high quality art that takes up a lot time and effort). If you’re willing to pay for one, here’s a list I wrote of some Instagram artists I’ve seen take commissions:
If you’re okay with an edited cover (free because of Episode assets), you could try browsing through various art shops and request from one that you really like. (: