classic motorcycle forum

I am new to this site but experienced over many years building and restoring bikes.  I do all my own work, mechanical and particularly electrical.  I hope I can contribute to the forums in a number of ways.  Currently I have a TZR250 1kt that I have totally rebuilt, a GS550 that I bought in boxes considerably chopped which I am rebuilding as a café racer and a Monet et Goyon Starlett 125cc.  This is complete and in 'reasonable' condition although I want to restore it to as new condition.  I now have NOVA approval with numbers and have downloaded the registration form.  This is the first import I have handled and among the many questions I am being asked to provide a 'dating certificate'.  I believe the bike to be first registered in France in 1957 but how can I get proof of this that the DLVA will accept.  I'm sure I'll have many more questions but this is the start.  Thanks for any suggestions.  I'll put some pics up later.