Yes, loads of aftermarket wheels fit. Most things with four studs and a PCD of 100 will fit with 'wobbly bolts'. Do a search and you'll find loads of options and information
Offset and centre bore are also very important but are quite aften forgotten. If a different centre bore is used spiggot rings may be required. Check here for further info http://www.carlsalter.com/wheel_fitments.html
In case you haven't already seen it, there is a classifieds section at the top where you can buy from other members - and usually if wheels fits one Fiat, it will fit another