Because NUmedia is a streaming media service, all the content we stream comes from the same sources. As a result it isn't likely that your local channels are not available with NUmedia. However there are a couple of other solutions. Depending on your area, you may be able to download your local channels directly to the fire-stick. Keep in mind these are apps that are separate from NUmedia and you'll have to exit NUmedia and go open that local channel's live streaming app.
Also, you can purchase a digital antenna that when installed in a separate input on your TV, you will be able to switch to that input and enjoy most local channels in the local area.