Orbi-tech.de is the only place I have seen ASA filament for sale and even they have only 4mm filament. I know it's possible to paint or otherwise weather-seal ABS too, but I don't know the details.
Polycarbonate (also available from Orbi-tech, at 3mm diameter) would be another option. That should be an extremely durable material. But you need a hotend that goes to 300C or so.
Polycarbonate (also available from Orbi-tech, at 3mm diameter) would be another option. That should be an extremely durable material. But you need a hotend that goes to 300C or so.