If you have the original English episodes (via legal purchase like Amazon or iTunes), you can download from sites like Subscene.com . Search for "Sonic Boom Season 1 Vietsub." The quality varies, but some community batches are excellent.
The show has rapid edits. Subtitles must appear and disappear in under 2 seconds. Poorly synced Vietsub ruins the timing. Sonic Boom Vietsub