^^Well buddy I feel the wheel covers Hyundai is offering looks best on the Eon.
If your wheels are not black then get them painted black and get the same wheel covers installed from the dealership itself,they make them look like alloys.
You can either ask the dealer to upgrade your rims to R13 or you can search for different wheel covers in market.Alto too uses 12 inch rims and hence there are a lot of wheel covers available int he market.
Go and buy the one you like.
Not only Alto's in fact you can get wheel covers for Eon itself.
Upgrading to R13s is a costly affair as you will have to change tyres too,for that money you can get alloys itself.Hence,I'd recommend you to either go for Alto's or Eon's wheel covers itself keeping your R12's as they are.