If you just want to polish it, use whatever you use on the hull. If you're looking to clean it, I haven't found anything that gets ingrained grime off.
I read on this forum some years ago that a product made for cleaning automotive aluminium wheels would clean masts up extremely well. I bought some and it had absolutely no effect.
I've no idea what it is like but Blakes do a mast cleaner product. The local Selden agent told me they use aircraft wax on the mast but in all honestly I'm not convinced they go to the trouble to polish it. Don't ask me where you get aircraft wax from though
Several years ago I used a liquid aircraft exterior skin cleaner on mast and boom which worked. Have not seen that one advertised again but do remember it was a Sedon agent who recommended it. A quick search for external aircraft skin cleaning brought up this. http://www.lastingshine.co.uk/acatalog/aircraft.html