Geography is an incredibly multidisciplinary field, so start your search in a multidisciplinary database, then try a few more databases from the lists below that suit your topic.
Because migration is such a multi-faceted topic, journals that cover migration are found in many different databases. Here are your best bets for finding articles on migration. Depending on your topic, other databases listed above might also be relevant for your search.
Add a few keywords relevant to your research to this basic search string:
(migrants OR migration OR immigrat* OR emigrat*) AND ...