i switched to coco husks but still use aspen for my smaller tubs and colubrids. i buy the big (24 quart bags i think) of Zoomed shredded aspen. previously i also used chipped aspen bedding by Kaytee or Living World (whatever was available or on sale). sometimes i mixed the shredded and chipped for a more textured substrate. anyway i always bought from my local mom and pop pet shop but i think u can buy them in bigger bulk sizes at Tractor Supply or other garden, farming, hardware store and such.