From my limited knowledge, The biggest thing you have going against you is the direction of the relationship. Since your relationship between the two databases is established in catalog 2, there isn't a reference field to follow from catalog 1.
In case it helps, here is some example code that will show related content from catalog 2 in a listing entry in catalog 1. Catalog 1 has a field called accessories that uses tags to list entries in a second catalog so you can select multiple related accessories for the entry in catalog 1.
Code:
<?php if ($entry['data']['product1_accessories']['value']): ?>
<?php foreach ($entry['data']['product1_accessories']['ref'] as $value): ?>
<?php echo $value['product2_name'];?> // Or whatever else you want to pull
<?php endforeach; ?>
<?php endif; ?>
Product1_accessories is a field in catalog 1, product2_name is a field in catalog 2.
Now, were I listing products in catalog 2 and trying to find the reverse relation into catalog 1, I don't know how to do that though I'm sure it's possible with some more in depth knowledge of php.
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