There are normally a few on ebay.
Don't just look for 59 mags, look at all the double stacks and you will find some that fit.
459, 559, 659, 610 and the 5900 series mags will all do the job.
In the communist state of NY, the mag must be destroyed or PERMANENTLY modified....... Uncle adheres to all regs; he destroyed it when the law was passed in the middle of the night........