Aka,
I have talked to the Nichicon, and they gave me the information is quite different from what you got.
For the RU and RY series :
Lead time : < 8 weeks
(no sample avaliable)
For the VR and VZ series :
Lead time : < 2 weeks
(if you need voltage <= 50V, they can have sample ready within few days)
I think it is quite reasonable.
(18 weeks? no idea....)

Sunny