Question related to Cardex

The Company manufactures chemicals which is stored, packaged and shipped in various sizes of drums. The Drums which have been procured over the period of time from various suppliers are being tracked as part of our Inventory (Cardex) as separate Item numbers. The customers use the chemical and send it back for refilling and the process is repeated until the drum reaches its end of life stage and hence forth destroyed or dumped.

Considering the business scenario, is there any way to find out the number of drums which may be there in market with customers at any given instance?