Personally I would use Jose Fransen now rather than CTA whose prices have risen….
Fransen want circa £245 euro for a headlinging in brown (brun) or grey or sell by the metre at 46 euro http://www.citroen-traction-avant.com/Content/C_Produkte.aspx?SPR=4&KATSEITE=065&Page=3
But interior restoration on a Traction isn’t cheap.
Personally I bought some hides from eBay http://stores.ebay.co.uk/Joshua-Oliver-Fabrics?_rdc=1 and made the interior custom rather than go ‘original’