Ducting question

Is there such as thing as a 10" to 6" reducer or do I need to combine a 10"-8" and an 8"-6"?

I found a good deal on a Can Fan Max 10" but I'm running 6" ducting since my tent only has 6" outlets.

Also, what is a good fan speed controller for this beast?

You'll need two reducers, which will lengthen the ducting. I don't know about the fan speed. See what works best. You want a nice breeze, but nothing too strong.