Howard has it right.
I have purchased over 10,000 ml of OEM inks this way. It is out there.
Large carts from all the bigger K3 printers (350/700ml) are usually available. We pull from 15 to 30ml of ink from just about any k3 cart that is supposed to be empty.
The more people that scuttle their older K3 machines like 3800,3880,4880,4900,7800,7880,7980,7900 + all the 44" models, the more ink will be available.
There is going to be a lot of this available with people switching to the new insets.
Wanting to stay with K3 inks is the main reason I just purchased a used 9890 and had a new head put in my 9900.
As far as ink dates are concerned I keep 2 machines with current inks (Within 2 years of the stamped cart date). My 9900 and P800 for critical work.
The other printers run almost nonstop for workshops and not critical work. (Do a fair amount of short term poster work, throw aways in about 3 months.
Not for everyone but you sure can save a ton of money! (I average a 700% savings!)