Most places in the world with metal flashing, metal gutters, or other metal on an exterior will have aluminum.

For gutters that magnets won't stick to it might work to use pairs of magnets.

1. Drop a strong magnet into the gutter.

2. Place another strong magnet on the bottom of the gutter under the place you dropped the aforementioned magnet.

3. Attach a ferromagnetic metal clip to the thing you want to suspend and use the magnet from #2 to hold the clip.