According to "Original Triumph TR2/3/3A" by Bill Piggott, TR3B's had only four standard colors and burgundy was not one of them. Apparently some were sent to the US with non standard colors. The factory did considerable experimenting with paint colors and didn't keep real good records. I'm unable to find any burgundy paint codes. If you aren't too concerned with originality, I would just pick out a modern burgundy color and go with that.
Tim