As with all these things it depends on what route you want to take with your bike, either ‘period parts’ that were available when the 900 was a current model or a remade modern equivalent which will give a slightly different look.
The latter if done well can still look good but many simply do not suit the classic lines of the original shape Monster in my opinion.
But second hand parts for the early (either carb’d or first generation fuel injection) are either getting hard to find, commanding high prices or require restoring back to their former glory (or a combination of those three).
As well as carbon, stainless, alloy or titanium there is also high or low level to consider, again depending on your preference.
Here are a couple that may be worth a look though:
https://rover.ebay.com/rover/0/0/0?m...2F233497385079
https://rover.ebay.com/rover/0/0/0?m...2F392717330692