If you right click on the track in foobar and select Properties, then go to Details and scroll down, you'll be given the loop start and end samples. If you need to convert them to timestamps, just divide the loop points by the sample rate (also found in the Properties menu). Using an external editor such as Audacity, you can trim a waveform converted by vgmstream to those exact points and copy/paste the loop as much as you desire.
Or he can just set vgmstream to loop a specific number of times(preferences/decoding/playback/vgmstream, set "Loop Count" to whatever, toggle "Loop Normally"), convert to wav or flac, then trim off excess audio in an editor.