To reach Clermont Ferrand you can fly in to Aulnat airport ( CFE) . Alternatively, you may fly to the larger airport Lyon St Exupéry , followed by a ~2h30 trip by train to Clermont ( plus a 1h tranfer from the airport to the Lyon Pardieu railway station by RhôneExpress tram) , or to one of the Paris airports. In this case, you should allow 1h, 1h30 transfer time to the railway station Paris-Bercy. The train trip to Clermont Ferrand takes ~3h.
More informations on the Tourisme Office webpages