I want to replace my ordinary wheels with alloys, how do I find out what will fit, it is a rare car?

Go to a tire shop that deals just in tires and rims. They will be able to give you all the info you need. PS I would not buy them at a junk yard. You never know what you'll get.Since I'm American, I will give you the US estimates. I would expect to pay about $ 800 for the rims and tires( you will also have to buy tires because the old ones won't fit unless you get 13 in rims.