Okay, so picking raw object names by expression is a bit fiddly. I suggest you put all of the JSON objects into a family. Create a family variable called index or whatever and do something like:
for "json" from 0 to jsonFamily.objectCount
pick jsonFamily where index = loopindex("json")
do thing
Alternatively you can use a single JSON object and instantiate it however many times you need. Then in the loop use JSONobject(loopindex).Get(".Value")