My quick tour through Google results turned up:
Facility Booking Module from Invenmanager.com
Booking Checkout Add-On module for Booking calendar from dnnflow.com
An Online Booking Module discussed here:
http://www.dotnetnuke.com/Resources...posts.aspx It also appears that Engage Software had a Booking Module. I don't believe it is available any more, but you could check with them.
There is some other booking software (doesn't seem to be DotNetNuke) here:
http://www.fileguru.com/apps/dnn_booking_module