Thanks again Jorge for your kind help.
In fact I use to buy most of my papers and chemicals by internet. There is some good resailers in Paris but for this particular item, I look for a Mexican store which could sell me some box of paper and send it to France. I am aware of all the problems I could encounter but as I told I have bought lenses in Japan and UK, chemicals in US, densitometer in Germany, and so on, all this with internet. I suppose it is also possible in Mexico.