You can use 240/260/740/760 and possible 940/960 wheels. Keep in mind the offset is different than the 140 series, but is usually fine. Or you can correct for it with custom wheel alighnment settings.

There are a number of US parts suppliers, but here in New Zealand the 140 was never for sale new. I import all my parts from www.scandcar.com, who can even supply very hard to find parts. They are close to the factories that made the parts for your car!

There is a lot of space for adding a turbo, but probably an all custom job required. Having the inlet and exhaust on the same side makes for interesting plumbing! Or you can go for a supercharger from www.v-performance.com, which I was told is better suited to this engine than a turbo (but don't have the knowledge to back this up).