IC for a 10nA Current Mirror
Just make a current mirror with a suitable op-amp, a couple resistors, and a low leakage transistor. 10nA +/-500pA is not very difficult at all under lab conditions.
You could (typically) use a BSS84 or 2N7000 (depending on the polarity of CM you need to make) at room temperature. For the op-amp use something with low Vos compared to the drop you can tolerate and (of course) low Ib.