Any free tool like xml-sitemap.com, will include maximum of 500 pages in XML sitemap. For more than 500 pages you need to make different files like sitemap1.xml, sitemap2.xml, sitemap3.xml and so on. NOw make a sitemap.xml file which include all urls of other sitemap files in same syntax. Then upload all in root directory. There are a lot of websites which offers sitemap generation of more than 500 pages but they are not free, you have to pay for using their services.