Is there an extension which can look for products with a given attribute in the user's cart and, if found, display conditional terms and conditions that only apply for those items? Or at the very least, display a configurable notice above the global terms and conditions.
I understand your question is related with https://community.magento.com/t5/Find-an-Extension-that/Avoiding-mutually-exclusive-products-in-same...
As I said there, probably you gonna need to implement your own solution.
Creating a product attribute could be an option to check if one product can be shipped with another one but I think you gonna need to create your module/customization to validate that part and block the checkout for that cart.
Perhaps, you can try the Custom Static Blocks by Aheadworks.
You can place custom blocks to shopping carts and provide particular conditions for that blocks, including narrow groups of products, but not limited to. You can also target certain customer groups.
Please visit the product page of the extension and its demo store:
Hope this is going to be helpful.