transportwindows .co.uk they make all sorts of doorr and windows for truck building and horseboxes etc, i have just fitted a pair of their doors exactly like you want, they come premade in the frame, cut the hole and rivit in. the come with locks as well, they make bespoke sizes or some standard stuff, i found one of their standard ones fits exactly, cost me £55 each plus vat and delivery, came in about a week, very well made
