You'll be able to get this one fairly early on in the game. Some quick tips:
- You'll already have crafted 1/3 by the time you get to Prosperity (you make a Saw Launcher on your way there).
- Level 1 weapons can be crafted with common materials (duct tape, gears, etc.).
- Materials are found all over - looting bodies, supply drops, and lying around various locations.
- As you explore, the map will show certain spots that have specific materials (e.g. Davenport Plains has 4 duct tape). You can also buy resource maps from the Cartographer or traveling Sherpa guy.
- I'd recommend crafting the bow as one of your earlier weapons because it's high-damage, silent, and you'll need it for the Archery Expert achievement!