Re: That is the problem with you guys, the FDA reported that many producers of Colloidal Silver had no silver at all.

Hi Grizz, 

The rule of thumb is to apply 1 mAh of current for every square inch of total surface area of the anode in solution(wetted). 

However, since this was formed to be overly conservative(safe), I prefer to keep things simple for all basic CS generator circuits such as those using two 12 or 14 gauge wires in a glass by using .5  mAh's current regulating diodes. And reserving the calculations for heavier applications. 

That said, any J503 Series Diode should suffice, and can be found at most electronic shops for a fair price(example only): https://www.futureelectronics.com/en/Technologies/Product.aspx?ProductID=J503LFCALOGIC1004973&IM=0

However, you can easily find single or small batches(5 or 10) of them on eBay at a descene price if you shop around a bit. As some sellers tend to grossely inflate the cost and where they likely only payed pennies per/pc in bulk. :/

A note on Current Regulating Diodes:
These particular types of Current Regulator Diodes can be had ranging from 0.24 mA through 4.7 mA with a 20% tolerance, and can easilly be paired-up to reach much higher currents with ease. ie, I currently run a circuit capable of 32 mAh using several 4.7 mAh diodes paired up together. 

You can also reach a specific current rating by mix matching several diodes together. ie, 1 x 4.7 along with 2 x .24 mAh's type of thing. And so they are very flexible.

Hope this helps,
And if you have any other questions or would like to see more diagrams etc, please don't hesitate to ask. :)