You may higher a freelancer to collect the names of all the competitors for you and then upload it to your Negative KWs list. 15.6 mm competitors won't be located in the same local area (unless your clients is a national campaign). In which case here a couple of additional suggestions:
1. Use Google maps contact extractor (super easy to find, use Google search). This grabs everyone, and fast.
2. Use a + (as in BMM style) in front of certain words in your KWs to avoid more name based search terms.