I cant help at all with any info on the Gardin brand of frame except to say that it's a very well knowname in France too.
As for the curved Excell seat tube, if it is a banana-shaped one, as opposed to the more usual compound curve, the tube is from Excell's Mexico series. If the tube has four decorative lines running longitudinally along the tubes, then the tube is from the Mexico Perle set.
Details of the Excell tubes and of frames made by Haral, in Savoie, France can be found at:-
http://www.flickr.com/
Norris Lockley
Settle UK