In regards with the calibration target, you should search for a white balance card (you could find plenty of them in Amazon). The problem with these cards is that they normally give the Albedo values for Red, Green, Blue. When they say for example 18% Gray Card, this means that they have Albedo values for Red (0.18), Green (0.18), Blue (0.18).
When you have a camera with different bands, then you should know which is the reflection of the material at each specific band.
This is a more complicated task. You should better check with the manufacturer of these cards. From our side, we are trying to find which is the reflection of the most common cards in different bands. Once we have more information, we will make it public.
We have found, for example, the following company that sells more complete calibration targets (they come with the albedo values in infrared too):
However, they are much more expensive.