The fête de vapeur won't be until 2012. They only do it every 3 years now as the organisation and planning is vast.
The last one was last year.
What is worthy is the MTVS steam weekend near Paris every October, You can go round the sheds and sidings as you please and photograph and measure everything. As most places in France they are very helpful.
I was going exhibit there last year and may do so this year if I can get a place under cover this time.