Where would one get a 17/64 box wrench?

FYI I tried a 7 mm box and it just spun. I did break them open with a 7 mm open end held cocked, but that seemed like a good way to strip them. I finally hammered an old 9/32 open end down to 17/64, and that fit. But the tolerances are really crappy -- it fits on some flats but not others. BTW I saved the old cylinders for rebuilding next time.