InfoPath Dev

I have a SharePoint list with about 5000 items which I need to use as the beginning of a cascading dropdown in InfoPath. I'm using SharePoint 365 and of course getting error messages about the size of the list. Is there a way to create a data connection to receive data that would first just retrieve the unique values of that very first dropdown? Or - what is the best way to handle this? It's a denormalized list of products, the locations they come from, and then other details like container size, weight, etc. If I could find a way to separate the locations from the product names it would cut the list to 1/4 its size. But - I need them connected so that the location can be selected after the product. Example: Product Location Container 1000 ATLANTA Bucket 1000 DETROIT 55 Gal Drum 1000 CHICAGO Bucket 1001 ATLANTA 55 Gal Drum

 I don't know if this is your issue, but when I was querying a SharePoint list, it only returned the number of items in the default view.  See if the default view for that list displays everything on the first screen.