yep red snapper.
http://www.redsnapperuk.com/camera-accessories/Monopod_Mini_Ball_Head.html#a39
use it with d300 and siggy 50-500mm os.
I can't speak for how well it'll support the lens because I don't have that one. But I've found the velbon RUP-L43 to be a great monopod for my d5000
Personaly I don't get on with ball heads on a mono
Yup, I really need three hands - one to hold the pod, one to hold the camera and one to turn the locking knob. I use RRS's Monopod Head - very expensive but a total dream, even with the heaviest lenses. For light stuff (up to 100-400, 70-200 f2.8) the Manfrotto 234RC2 is OK.
You not tried the Manfrotto 322 on a monopod?
Er, no! Even without my arthritis I wouls still despise joystick heads.