Like Berkman said, Keithley make very low current meters, they should have a lot of info. How low is low for you?
Other sources are the company that make fA op-amps. In my days, Burr Brown had a lot of app. notes also. If you get down to pA range, it can start to get tricky. Also check Analog Devices, Maxim and Linear Technology. I never seen textbooks talk about measurement, you have to go to app notes for that. I learned from Burr Brown in the 90s. But I don't know whether they are still around, might have been swallow up by AD or other companies.
Regarding to current mirrors, do you mean circuit use inside ICs that use a transistor to setup the bias for other transistors to scale the current. If so, I doubted there is a book specialized on this as it is quite simple, only deserve two to three pages of materials. Look at any IC book and you find info about this.