Ebay is your friend in this case. I won’t link to a specific store but (at least in the UK) there are a bunch of sellers with a lot of items sold. I brought a replacement LCD just last week from there and it was fully functional.
The 2DS XL does need the top screen ribbon cable inserted to turn on at all, I’m afraid. It can turn on without the speakers plugged in or the camera ribbon cable in (the one on the back of the case that you have to unmount to remove it) but everything else needs to be hooked in.