"YOU ARE CORRECT, ARISTOCRAT. FIRSTLY, MAKE SURE THERE ARE CREDITS REMANING ON YOUR CYBERNETICS CREDIT WEDGE. THE INSTALLATION OF A CYBERNETIC IMPLANT COSTS ONE CREDIT." - Cybernetics Terminal when asked about "HOW DO I INSTALL A CYBERNETIC IMPLANT?"
A Cybernetics Credit Wedge only weigths 1 lbs and holds one credit.
There is a guarenteed Cybernetics Credit Wedge on the 13th level in Bethesda Susa on a random location in the level. The use of AOE weapons is not recomended if you want to acquire it.
It is possible to find others as random treasure, especially deep in the underground (around a depth of 20), but they are extremely rare, so you shouldn't rely on finding one in this manner. If you desperately need more, you can also use Metamorphic Polygel to copy the one guarenteed one - but make sure to do so before spending the single credit on it!
The best way to acquire cybernetic credit wedges is to perform the water ritual with an elite Putus Templar, you may ask for one for 50 reputation.