Adobe has recently released a new "Distinct Count" segmentation feature that allows building segments on counts of dimension (eVar/sProp) values. I would probably use segmentation on a distinct dimension count to solve this. Here is demo video for more details. Segmentation on Distinct Dimension Counts - YouTube
This still doesn't seem to get at how many orders had 2 units of a given department in the order. For example, Dept A showing 25 orders with units greater than 1 does not guarantee that the orders had 2 units from that given department. It just means that 25 orders had at least one unit from Dept A and also another unit (from Dept A or another department).