Although Alfa Romeos haven't been sold in the US since the mid-90s, finding parts for them is quite easy and relatively inexpensive, even compared to common cars like Toyotas. Here are some popular places to get parts:
There's also an excellent support network at the Alfa Bulletin Board. You can see recommended Alfa repair shops here...and as a Google Map here. As you can see, depending on where you live there are quite a few shops to service your Alfa. Alfas are also easy to work on if you have the desire to do that. Later models have Bosch fuel injection and ZF hydraulics, so they are quite reliable.
Its expected that Alfa will return to the US in 2013 - 2014; that will be interesting, possibly increasing Alfa values as awareness is increased and people see the beauty and soul of these cars.