In the z39.50 search targets editor, add a field for “item tag”. In the case of searching a Koha target, it would be 952. We’ll have to find out what the item tag is for other ILS’s. It seems 852 and 949 are common.
Modify the code to count the number of instances of the given tag for the given server
Show this number as the “holdings” for the given search result.