Hello.
You can go to: https://www.odoo.com/apps and download apps manually. I'm not sure if all of them are going to work since Odoo is making changes these days but you can give a try. You have to put the folder of the module on addons folder. Or you can create your own folder and add that folder to your "addons_path" on openerp_server.conf.
To install these modules you've to give "Technical Settings" permission to your user. And then you have to refresh your browser. You're going to see a link under Configuration named "Update Module List". You've to update your module list from there and you're going to have that modules on your system.