Are you fine with a 11.2 update backup? Because theres full update packs up to that version with a quick google search. This requires the good old SysDowngrader instead of the CTR Transfer.
You just need to go to that "chaos" site. Since that "iso" site hasn't updated its updates since 10.3. Sorry but thats your only choice. I would've PM'd you a CTR Transfer of my own 3DS but I only own New 3DS consoles.