I recently refinished a steering wheel on my project car. It did have some small pieces that were loose as with yours. My method was to use JB Weld to glue the pieces back on and to fill any other cracks and chips. It sanded out very nice and smooth. JB Weld has very fine steel particles in the mix for reinforcing and I've always found the stuff to work very well.
A very close paint match is Rustoleum Satin Ivory Silk 249073. Front of the can says Bonds to Plastic. Covered with their Gloss Clear 249117. Perhaps not as good as a quality automotive paint but easy and the price was right.
A general word of caution on removing Amphicar steering wheels as they can be difficult to brake free from the tapered shaft. It's necessary to place a bearing separator (like this Harbor Freight one) under the center metal hub and pull on it using a bearing puller against the steering wheel shaft. It's tempting to place puller arms directly on the center (plastic) area of the wheel with damaging results. Those two ovaled looking holes appear to have been added in an attempt to remove the wheel.
http://www.harborfreight.com/automotive-motorcycle/pullers/large-bearing-separator-3979.html