Uh, that is unfortunate. You are going to visit beautiful country and you will not have any guide to show you important things. Yes, I also heard that it is the dead season in December. So it is a very good question :where to find Bangladesh Tour Companies in December? But maybe if you go there on the beginning of the month some agencies will be still open. Or maybe they never close, and they work either is season or not. But you can always buy one of those book guides that will help you to know what places should you visit.
I am going to spend some time in Bangladesh in December. But I heard that December is dead tourist season for them. So I am interested to find out where to find Bangladesh Tour Companies in December. I would like to hear if someone had similar problem, and how he/she solved it.