I want to implement a third party or custom crafting system into my dnd game.  But, this requires a host of new mundane inventory items such as, leather scraps, cured leather, regenerative reagent, etc.  I don’t want my players to have to add each of these items to their inventory as custom items, that would get old fast.  I’d like to create all of the items myself, then allow them to search for the item by name and add it to their inventory just like normal inventory items from the phb.  Is there a way to do this?  

I don’t think there is a way to make mundane items like you would want. Could maybe you use homebrew magic items for these? like wondrous item, and name them whatever they like. Keep the rarity common, unless you want less common, and name them Leather scraps, etc.