Source an internal/hub derailleur for Bianchi Bergamo
You could order your own replacement hub, for example Universal currently lists the 36h Dual Drive (Disc) for $187.  These hubs are a relative rarity, and I don't doubt that your LBS price would be above $300.  Bianchi presumably got them in bulk for a bargain when they specified this frame.

If you're carrying heavy loads upgrading to 36h is certainly a reasonable solution and will definitely help.  You can also select a beefier rim - I personally like the Salsa Delgado, but rims such as the Velocity Dyad and Sun Rhyno Lite are perfectly fine as well. Lastly, get a professional wheel build.  All told you're probably looking at at least $320, most of which is dominated by the price of your hub.

Depending on your riding conditions and preferences, another solution might be to replace your Dual Drive hub with a normal 9-speed derailleur hub. This will cost a bit more than usual in the near term (you'll need to replace the shifter and the derailleur), but you'll have more wheels at your disposal.  Craigslist and eBay can be a treasure trove of relatively inexpensive handbuilt wheelsets, if you're patient.