There isn't a non-sourcemod addon that allows for survivor legs, yet. Well, there is one but it doesn't work with custom weapons and survivors.

Here's a sourcemod plugin that has them, though: https://forums.alliedmods.net/showthread.php?t=299560

And an installation guide for sourcemod can be found here: https://wiki.alliedmods.net/Installing_SourceMod

The mod that I mentioned can be found here if you don't mind missing out on modded weapons and survivors: https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=782616059

wheres the legs from l4d1?