Unity-Source-Tools
Plugin to import resources from the Source engine in Unity3D.
Instructions:
Step 1: Load scene respective to what game you are extracting from, and click the WorldManager gameobject.
Step 2: Set the Export Location to where you would want to export the map.(This is optional)
Step 3: Set Map Name to the name of your map you want to import.
Step 4: Set Model Name to the name of your model you want to import(untested).
Step 5: Tick "Load Map" or "Load Model", depending on what you're doing.
Step 6: Tick Skip Sky. Otherwise, your sky will be full of garbage.
Step 7: Scroll down to uSrcSettings.
Step 8: Set the Path to wherever your game folder is(example: D:\SteamLibrary\steamapps\common\GarrysMod )
Step 9: Depending on what you're doing, adjust the game, have mod, and mod settings. 
Step 10: Tick Textures, Displacements, Props, Props Dynamic, Entities, and Gen Colliders. Do not tick Lightmaps.
That should work! If I got this wrong, please leave an issue.
Original Readme Below
Author: vk.com/lewa_j
VK Public: vk.com/uSrcTools
Supported formats:
bsp - maps
vmt - materials
vtf - textures
mdl - models
vvd - models vertices
vtx - model indices
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uSource UnitySourceTools uSrcTools