Is it possible to override renderer used by h:selectOneRadio?
Yes, surely it is. Otherwise, UI component libraries like PrimeFaces couldn't exist.
I tried to find the class from jsf-impl package but didn't find it.
The exact class depends on the JSF implementation you're using. If it's Mojarra, then it's the com.sun.faces.renderkit.html_basic.RadioRenderer class. If it's MyFaces, then it's the org.apache.myfaces.renderkit.html.HtmlRadioRenderer class.
In order to properly override it, just extend the class and override methods where necessary and register it as follows in your faces-config.xml:
<render-kit>
<renderer>
<component-family>javax.faces.SelectOne</component-family>
<renderer-type>javax.faces.Radio</renderer-type>
<renderer-class>com.example.MyRadioRenderer</renderer-class>
</renderer>
</render-kit>
Keep in mind that you're this way tight-coupling the renderer to the specific JSF impl/version. Such an extended renderer is not compatible with a different JSF implementation (i.e. your app wouldn't deploy when you ever replace Mojarra by MyFaces) and may possibly break when the current JSF implementation has been updated to a newer version. If you worry about this, consider writing the renderer entirely from scratch, like PrimeFaces et.al. do.
The reason I want to do this is to get rid of the table it generates.
Consider looking at Tomahawk or PrimeFaces instead of reinventing the wheel. They have respectively a <t:selectOneRadio layout="spread"><t:radio> and <p:selectOneRadio layout="custom"><p:radioButton> which allows you positioning those things everywhere you want.
See also:
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