Parts are often available through owners clubs and ebay. These bike are becoming collectable in Italy now, so prices for parts are going up a bit. There are quite a lot of NOS parts around from the main USA dealer: Cosmopolitan Motors who went out of business a few years back. Some parts are rare as hen's teeth: gear levers, oil filters for example. Most of the electrics are CEV so easy to source. There is a good Motobi Facebook page which details an engine strip with good photo's.
They are straightforward to work on and only require a few special tools, all of which are easy to make yourself. I have some spare parts that I sell from time to time: Pistons, cylinders, tank etc, but I expect the shipping from the UK would be rather high. Some on ebay now: seller name is nick3395
Parts manuals and workshop book are available for free on the 'net.
I'd say it's worth buying as they are fun to ride and easy to work on.