How to Sync a MySQL DB with a Oracle DB?
Oracle GoldenGate might not be useful for you if Oracle source database is outside of your organization with no possibility for you to set up extract process.

The best for you is to have a look at this old post "Migrate from Oracle to MySQL" that despite its title points out good ways to do what you're looking for.

I found especially useful the below points from David Mann answer to the above mentioned topic:


There are 3rd party utilities available. I have used a few of these
but best for you to check them out yourself for your intended purpose.
A few 3rd party products are listed here: OraFaq . Unfortunately a lot
of them run on Windows which would slow down the data unload process
unless your DB server was on windows and you could run the load
utility directly on the server.
If you don't have any complex datatypes like LOBs then you can roll
your own with SQLPLUS. If you did a table at a time then you can
easily parallelize it. Topic has been visited on this site probably
more than once, here is an example: Linky