You can obtain Russian visa in the country of your citizenship. You need to get in touch with the Russian consulate in your country and make sure that your application will be accepted.
Please indicate the subject of the email as Visa Application.
For invitation from the committee you can also fill the form http://www.apply.volsu.ru/ru/apply , where you have to mention that you are the 'Guest of the University', all the applicable data, and write the details about your event in "Additional Information" (e.g. - participation in the 8-th International Scientific and Practical Conference “Current issues of linguistics and didactics: The interdisciplinary approach in humanities and social sciences).