We have found 6 bags that match these dimensions.
21.5x13.5x7.5"
linear: 42.5" 35L
The bags below are not exactly the size you were looking for, but perhaps you'll come to like them.
20x12x6.75"
linear: 38.75" 28L
21x12x6"
linear: 39" 28L
46x29x20cm 18x11.5x7"
linear: 95cm/36.5" 24L
19x13x5"
linear: 37" 22L
42x34x11cm 16.5x13.4x4.3"
linear: 87cm/34.2" ~16L