This collection features weapons, that are only supported by the WORK IN PROGRESS version of the WeaponsWorkShop mutator and currently not featured in the normal version until its next update.
The WeaponsWorkShopWIP comes with the subscription of the normal version and also features all of its supported weapons.

Link to the mutator: http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=147258902
Link to all fully featured weapons: http://psteamcommunity.yuanyoumao.com/workshop/filedetails/?id=147289850

Notice that you can add unsupported weapons manually with the mutator. It's just not as comfortable as this.