If it is uploaded to battlenet then you can reference it directly from that. Otherwise you will need to open the mod, extract the model and place it where you want to use it (in the map, or a mod used by the map preferably).
🔨 Hive's 3D Viewer has been updated! 🔨 It now supports MDX1100 which should fix a lot of issues when viewing HD models in our 3D Viewer. We encourage you to check it out for yourself and report any issues you find in the Site Discussion board.