Any alimentation shop? Cayenne is not something exotic that you cannot buy it in Migros, Coop, Manor etc.

I see; I'll try there then.

thx.

If you will be contining after your first bottle of syrup, or for a next time, it's not a bad idea to buy organic syrup as certified organic farms have to adhere to stricter regulations concerning lead in equipment, types of filtering agents, and bans on chemical defoamers used for processing the sap into sugar. And have to work with certified foresters to ensure the sustainable management of  forestland, promote tree health and biodiversity, and reduce erosion. 

I've bought this one:

http://madalbal-versand.ch/neera-sirup-zitronensaftkur.html

which one do you recommend?

I can't recommend a make. You would have to go into a bio/organic store and see what they have. That's what I did. There is a possibility that it mght be a little more exensive, but I'm not sure about that. I have never compared the prices.

At which bio/organic store did you go?

I would think you would find it in most. 

I don't know bio/organic shops in Lausanne area/Vaud. Maybe someone else here would know?

Sorry to rain on your parade but these detox diets are abolutely useless. There is not a single piece of scientific research that shows that these diets are effective. It's just a combination of theory and marketing. If it were so easy to detox your body, people who have ciguatoxin from eating the wrong fish would go on one of these miraculous diets to get rid of this very annoying toxin. Doing this lemon detox diet for one week is a bad idea for your body, sure you will loose weight but you will get it all back (and more) shortly after.