Dear Ms. Moller,
Thank you for posting your request on History Hub!
Sources of useful information are the YIVO Encyclopedia of Jews in Eastern Europe articles about The Pale of Settlement and Cantonist Law regarding Jewish Military Service in Russia. Another resource is the Jewish Virtual Library article on Cantonists.
We suggest that you contact the Federal'naia arkhivnaia sluzhba Rossii (Rosarkhiv) [Federal Archival Service of Russia], ul. Il'inka 12, 103132 Moscow, Russia.
We hope that this is helpful. Best of luck with your research.