I was just looking up some options yesterday (wound up getting a hori split pad) but if you want to be able to use the joycons w/ a flip grip, this could maybe be a cheap and easy solution.... not sure how great it works:
https://www.amazon.com/Skull-Co-Button-Nintendo-Switch/dp/B07LGF9WWY
It’s a dpad that you literally stick over the existing buttons lol. Reviews says the pivot isn’t great, sounds like it might not make firm enough contact w/ the joycon body. If that’s really a problem, and not just improper attachment, I was thinking it could maybe be padded out with little pieces of electrical tape.
edit
OH, just remembered I also found this guide to putting an actual Saturn dpad on a joycon a while back, but it’s more modding then I really care to get into: