Basically you have to provide a link to the search form that returns your web pages (probably as a tar or zip file). Google for "MIME" and look for an appropriate reponse, for example "application/zip" for a zip-file should work. (See http://de.selfhtml.org/diverses/mimetypen.htm for a nice list, german but easily comprehensible).

Behind that link can't be a static file, because the web server still has to download those pages, which takes time. A static link would just return file not found. So instead you need a CGI script behind that link that delivers the result of the mirroring and zipping as soon as it is available, with the appropriate MIME-type

I don't think you can deliver the web pages separately without much complex scripting and you also can't avoid that the user is asked where he wants to save the file, except if he has configured his browser to just save files of this type to disk without question. That is outside your influence