Hello @PBUSCEMI and welcome to the customer community. Thanks for reaching out. First, as an IM customer, please make sure you are adding your content in IM and publishing to your trading partners like Kroger. From there, you will top off your attributes for Kroger in VIP and submit when ready. You can learn more about that HERE.
For your actual question, this can be challenging sometimes when the original information provider does not have all the information you need to sync that content with your trading partners. You could talk to your information providers and check to make sure they do not have case GTINs for the consumer units and if they do not, ask them if they can provide you GTINs you could use based on their prefix/UPC of the child item. Since some of these companies are smaller, as you mentioned, if they are not familiar with how to do that, you could ask them to let you create case GTINs based on their UPCs but that is a grey area that you would have to navigate carefully with them. You would need to share the case GTINs with them so they know that number is used.
