Tamron nestar 400 mm lens ?

Hi all, might be a bit of a long shot, but does anybody know anything about a Tamron nestar 400mm f6.9 lens, it's in a K mount, what you might think it's worth,
cheers
Dave

It's quite easy to find 400mm lenses with an aperture of f5.6. Personally, I wouldn't want to buy a long lens as slow as f6.9.

G