I have been trying to find the answer to this, but I have been struggling.
Finding an English copywriter is far easier than finding a copywriter for another language. Web copywriting is not just checking the language, but making it suitable for the web, which complicates things further.
What would you do if you're language ranked 64 on this list - http://en.wikipedia.org/wiki/List_of_languages_by_number_of_native_speakers?*
What would you do if you're language ranked 64 on this list
Network within the community speaking that language.
You are right. Sales letters should not be translated, it'll have to be recreated to have a good chance at working.
I have no luck. I search a couple of sites and all I can find is proof readers. Maybe this can be enough, who knows? There are many proof-readers here, just nobody really specializing in web. I am not sure if this will be a problem.