Large supermarkets could help you out as I understand they sell off empty cartons to some companies that do the recycling. There are two supermarkets near my home and I have observed they have a special place where such boxes are kept to be disposed of later. Talk to the people there and may be you will run into some luck. If you are looking for new ones, just google it under "carton boxes suppliers in Doha" and you will find a list of manufacturers along with their contact details.