DH1758 teleconverter for SEL55210: alternative recommendations?

Hi -

I've seen several recommendations for the DH1758 1.7x teleconverter (to be used on an SEL55210 Sony NEX-6 lens).

Unfortunately, the DH1758 seems to be discontinued.  I've tried several sites that claim to be selling it, only to find out that it'll be "backordered" for several weeks.  I don't have much hope of them ever being able to deliver.

Can anyone recommend a good alternative teleconverter?  At least 1.7x, but 2.0x would also be nice.  These places I've tried ordering the DH1758 from have told me that they have 2.0x, 2.2x teleconverters from other manufacturers, but I don't know if they are any good/how well they will work on the SEL55210 lens.

Or, does anyone know of a place in the US where I can get the DH1758?

Thanks in advance for any recommendations!