Consider transferring the whole directory instead of individual files:
scp -r username@remote:/remote_path /local_path/
If that would transfer too much and you really only want to transfer the files whose names ends with .json in the single directory, you may want to consider rsync (which has better facilities for filtering what gets transferred):
rsync -av --include='*.json' --exclude='*' username@remote:/remote_path/ /local_path/
This would only copy files whose names end in .json but ignore other names. The terminating / on the source is needed here.
The -a option makes the transfer also transfer file meta data (timestamps, basically) and makes rsync recurse down into subdirectories (but this is restricted by --exclude above), while -v is for verbose operation.