It will depend on the details of your mapping solution, how it tags items as display cards, etc, but in general this approach should work;
Prep. Make your collection list item contents a component, create the properties, and bind it those properties to your collection list.
Duplicate. Now clone the entire collection list 2 or 3 times ( once per 100 items )
Range. For each of those, set the range settings. Collection list #1 starts at 1. #2 starts at 101, #3 starts at 201…
This will give you all 300 to 400 cards in the page, for your JS for the map integration script to access.
Important- if you ever filter or sort your collection lists, make sure to use the same filtering and sorting settings an all of them to avoid duplicates or gaps in your output.