If you are looking for a great place to find cork bark round and flats make sure to check out Pangea Reptiles! I bought something crazy years ago like maybe 60lbs of rounds and flats and I still have them today. Corkboard is really amazing because it lasts a very long time and provides a place for a gecko to hide or sit on.
I like to cut flats to size and use as perches. If you cut to size then it just holds itself up! With rounds, my mentor uses a 2 inch circular saw and a drill to make holes so they can get in to hide and get out.
After a while you will want to sanitize them by washing with soap and water (I use dawn) and then allow them to dry in the sun.