Pivot to track products that are predominantly sold to one customer

Hi

We are looking to track items that are predominantly sold to a single customer. This is to reduce the risk of excess stock should the customer stop purchasing an item. 

I have a data set showing item sales over financial year

Date, Customer No & Name, Item Name & Desc, Quantity, Amount

Currently, I have a pivot table with a time slicer showing sales that have been made to a unique customer (added data to data model and used distinct count) which shows

stock item, description, qty sold, value sold

This shows items that are purchased by a single customer and is working well. 

However, I am looking at enhancing our reporting to show items where 90% of an item is sold to a single customer. Using customer count and sorting gives me items that have been bought by small numbers of customers but does not help show any skew/bias of sales of an item to a single customer 

Thanks for any help. 

Willy