Please let me know are they Inventory Items or expense items.
Expense Items is not necessary to define in Inventory.
The Possibilities are as follows
a) Items can be derived from the Blanket Purchase Agreements (Using Bulk Load)
b) Items can also be viewed in the Punchout Stores.
These items when seen in iProcurement, observe that the Internal Item Code field in the Search result will be blank.
This means even though an Expense Item, it would be searchable from the store.
The information flow is unidirectional, meaning all items of Inventory satisfying the conditions (Purchasable flag checked, Unit Price valid and Expense A/C valid) will be visible in iProcurement but all items in iProcurement need not be visible in Item Master form.