Bitmain may sell some down the line.  Ditto Avalon.  If you check out the usual Chinese marketplaces, you might find some older Avalon and A1s pop up there.

The only open offer I'm currently aware of is the SF3301 through dualminer.com: http://www.dualminer.com/SFARDS-SF3301-40-chip-package_p_34.html
There's at least one other forum member who has worked with those chips (J4bberwock).

Though if you have $300k to throw at the problem just for chips, you should probably just contact the manufacturers directly and see what stock they'd be willing to part with.