Measure the inner diameter of your wheel hub. The outer diameter of the mounting hub on the elantra is 67.1mm.
So, for example, say your wheel's inner diameter is 71mm. Then you get a hubcentric ring of 71mm outer diameter and 67.1mm inner diameter. I'm sure jcwhitney or summitracing sells those. You can also get these from any decent local wheel/tire shop. they can even measure it for you and get the right one.