1) First talk to the Felyne that creates equipment designed for Felynes
2) Select "Aquire Scrap Items" [Second Option]
3) Select to Aquire Scraps from your Bag [First Option]
4) Make Scraps
5) Immediately open your bag afterwards. And the item you chose to make scraps would still be there, and the scraps made will also be placed inside your box. To avoid this glitch, simply choose to make scraps from your box [Second Option] instead of the [First Option] from your bag. The item that you made scraps from should still be there.
Repeat this method to obtain a infinite amount of a specific scraps.