If a integrated supplier does not have the +Add Item button on their Order Guide,
then you can search from their catalog.
If the Supplier has a + Catalog option on Cut+Dry,
you can add items through their catalog.
Search for the product you are looking for by scrolling, Filters, text input, or any methods combined.
Using the + to add the desired items to your Order Guide.
Once added successfully the + will change to Added to Guide.