Finding gaps in a Pivot Table
 

I've created a pivot table that filters warehouse bin locations into
alpa-numeric order (such as B01A02, B01A03...etc). When a particular bin is
empty that location is skipped altogether, but that information is useful for
knowing what bins are available to receive stock. What I would like is a
formula that would find gaps in the sequences and report where there are gaps
and how many empty bins are available. I imagine a column listing empty bin
locations and then a total for the number of empty bins. Does anyone have a
formula that could produce something like that?