How can I find a replacement LED to repair RJ45 tester? (re: SMD size, measured with multi-meter)
You do not need an LED with the exact same current rating. An over-rated LED will work fine.

Furthermore, indicator LEDs are not usually driven with the highest possible current, so it is unlikely that you even need to consider the drive current at all, and almost any LED of the correct color and package will do.

The exact brightness, color, and beam pattern might vary; if this bothers you you could choose to replace all the LEDs, even the working ones, so they are consistent.