You could always just buy more and more cables, cut them and twist them together and put electrical tape on it to hold and then continue for as long as u need it lol
But extension cords :P
I'm pretty sure a 25ft iphone charger doesn't exist for the reason that sane people use power extension cords instead. you can ofc see in apple.com->accessories to see, but..
You can buy like 5 chargers and with some electrician skills you can probably put them together, I'm just repeating what everyone else said, cus that is what you do on this forum.