I never played the Facebook version but I did play the mobile version a lot about a decade back, before the graphical changes and Heroic Races. I never got the chance to check out the Facebook version (I was five at the time lol.)
A lot of restoration projects for old webgames exist online, but like you said it unfortunately doesn't seem like anyone's making one for Dragon City. That being said, it is 100% possible to start one yourself. Usually restoration projects gather cached data from previous webpage visits across multiple contributor computers and compile them into a playable version. It requires quite a bit of manpower, technical know-how, and an untouched clear cache button (thankfully most Facebook uses are old and have no idea where that is lol), but it's definitely in the realm of possibility. It's quite an undertaking though, so other than that, you could search for an older Dragon City APK. It would be for the mobile version, but it's a good compromise regardless.
This probably won't be playable due to login walls, but checking the Dragon City page on Wayback Machine might also be worth a shot. Even if you do get walled, Wayback should have quite a bit of the game's inner-workings + graphics stored within the archived page's source. Reaching out to Socialpoint themselves, might be a bit useful depending on their policies, but I wouldn't count on it. The Dragon City wiki seems to have quite a few ripped graphics from before the art update too.