The last place i ordered mine was 3rivers. I tried the bamboo they advertise as heat tempered and flattened, just glue on. Don't waste your money. Its not worth it. I still had to do about 45 min of work to mine to get it ready to glue up. The next few pieces i order will be from Mike at Dryad bows. He is a sponser here.
To get it thin i run it through my bandsaw or table saw to take most of the thickness off, Then stick it in the hotbox for a few hours. After its out of the hot box i'll finish thinning it on my belt sander. Then its ready for glue up.
There is a good video on this if you search for bowstick archery. He goes over the whole process. Hope this helps!
Adam