When I was still working as Food Research Assistant, we conducted two studies: Barako Coffee in Filter Bags and Herb Coffee Flavored Coffee in Filter Bags.
The problem we encountered was purchasing filter bags. This might not be as hard if we had the budget cause purchasing it from possible suppliers would be easy. Unfortunately we don’t had the budget for the costly packaging.
As an alternative, we purchased a cloth called “pilon”. We chose the thickness enough to hold coffee grounds and provide a good water permeability. This cloth can be sealed with a heat sealer. Take a look at bottom picture.
Pilon cloth can be bought from Divisoria or from any cloth store.
The manual method of making filter bags is suitable only for experimental processing. Ask a friend mechanic or a nearby machine shop to fabricate a low-cost packing/sealing machine.
Ma’am Fe N. Dimero told me that a tea store inside Farmer’s Plaza Cubao is selling tea filter bags in small quantities. She forgot the store name (sorry!). If you are living in Manila, Quezon city and other nearby provinces, going there and finding the store may not hurt.