Does anyone sell negative impedance converter (NIC)?

[Moon Winx]

Preferably metrology-grade? I can't seem to find one commercially available, and I'm no electronics expert so DIY is out of the question until I learn more. I've seen various circuit diagrams and simulations but none actually realized/tested. I'm basically looking for a device to supply (ideally) all current across an unknown load for an attached voltage source. In other words, there should be no current draw from the voltage source (in reality, there will be some minimum current draw, but perhaps in the uA range for 1 V over a 50 ohm load). I've simulated a NIC and with the correct value feedback & divider resistors and it can do exactly that. Perhaps there are other designs/devices that could do that as well, but I'm ignorant on that.