The closest thing I can find to a 600 mfd is a 550 mfd at 385 volts. If I have to, I can tack in a 47 mfd alongside the 550.
See here.
There is also an 800 mfd. Which would be better? I've heard it's OK to go up, but I don't know about almost double the value. Wouldn't it make the B+ too high?
Here.