This might be a pain in the ass, but I recommend checking the Wayback Machine. If you go into the URL section of a Twitter account link, you can find a list of all individual tweets prefixed with that URL that have been saved, meaning if you're willing to take the time and energy to sort through them, you can find most, if not all, of his artwork that was ever posted on Twitter if saved on there.
Though be warned: Kerorira has 4, 782 URLs saved, and there's no guarantee they will all be artwork or non-retweets. And unfortunately, I've yet to find a method besides manually checking all of them. But if you are willing to take the time to look through them, it is well worth it.