Unfortunately, the market is probably flooded with hybrid amazons, and no one realizes they *are* hybrids. There are two different types of blue fronted amazons which have been bred together. People realized they were different, but they thought it was just a color difference, not a difference in subspecies. Some people think Orange Wings are blue fronts, and then we get hybrids like the bird pictured below in the link...
Orange Wing x Blue Front Amazon Hybrid | Flickr - Photo Sharing!
Not to mention two different subspecies of orange wings... Then we have the Yellow Crowns and all their subspecies... Yellow Crown, Panama, Yellow Nape, Yellow Head, Greater Yellow Head, Tres Marias... and people have once again hybridized these amazons either because they couldn't tell between the subspecies, or they did it for color.... yet again, not realizing they are creating hybrids.
City Parrots (on Flickr) has some photos of Urban Parrots - including hybrid amazons....
Flickr: Search Hybrid Parrots
Flickr: Search City Parrots' photostream
I have photos of an amazon of an unknown species, might be something like a yellow nape x blue front hybrid (no photos showing his nape - might be some on my computer... forever lost?)
http://img.photobucket.com/albums/0903/MonicaNFids/SF/AJ/P1010018.jpg
http://img.photobucket.com/albums/0903/MonicaNFids/SF/AJ/P1010007.jpg
http://img.photobucket.com/albums/0903/MonicaNFids/SF/AJ/P1010006.jpg
I think it's good for birds to have companions. With a few exceptions, parrots live in flocks. It is unnatural for birds to be single companions (not to get into detail about how everything humans do is unnatural...) That said, two birds is more work, and there is the chance of losing your bond with your bird. If you want to get another amazon, you need to try and weigh the pros and cons against each other and decide if that's the route you want to take.
Never expect two birds to get along, even if they are the same species. Expect the worse and hope for the best!
BTW, some birds may identify with another species better than their own if they were raised in a mixed flock kind of setting rather than kept with their own species.