Hi flamsteadflicker - Welcome to the Sony Forums 
While I do not know any specific information about the release of this lens, I can tell you that 'currently unavailable' is the default status when an exact date has not yet been set for the release of a certain product. Having said that, looking at various other online stores through Google gives a date of between 1-3 months so I would advise you to keep checking the Sony store as well as other online retailers regularly.
Thanks,
Simon