A program like VIDE could really help you. Just select the Pakfile lump editor, choose your .bsp and add the tf folder path (C:\Program Files (x86)\Steam\steamapps\common\Team Fortress 2\tf <----Should be this on 64bit windows)
If you have your assets in the custom folder VIDE won't pack them but to fix that just change the path to C:\Program Files (x86)\Steam\steamapps\common\Team Fortress 2\tf\custom
After it has finished searching for assets after you click scan and put the folder path in, click auto. This will automatically select all the models and textures needed for your map. Then click apply and the files should appear highlighted in orange in VIDE. Scroll through them and see if you have everything and if you do, just hit save. The files should be highlighted green after that and it will save a copy of your .bsp with the files packed, but it also saves an unpacked .backup just in case