Well for HD Gravity Guns, check out some of the weapon packs. I think the HL2 DM page might have some skins as well. There's also the Steam Workshop but you have to know how to unpack GMA files. There is one skin in particular that I like https://facepunch.com/showthread.php?t=1567488 last I checked this does have a HL2/Episodic version that works. TF2 style, I honestly don't remember coming by one. Reanimation, one of your best bets is to check the weapon packs. Hope this helps.