I would look online, or if you have any dairys close you could ask where they get theirs. You could also check out the xlarge plastic dog houses, full size goats fit in them so they might be OK for a couple of lambs.
You should definitely look online. If I google Calf Hutch I find several manufacturers. They have contact information where you can find dealers, or they may ship direct.
You could probably house two lambs a lot cheaper though.