We have found 21 bags that match these dimensions.
50x29x20cm
18L
The bags below are not exactly the size you were looking for, but perhaps you'll come to like them.
47x26x14cm
36L
48.5x28x16cm
26L
46x29x20cm 18x11.5x7"
linear: 95cm/36.5" 24L
39x25x20cm
23L
47x27x17cm
~22L
40x25x20cm
20L
19L
40x28x16cm
linear: 84cm 18L
40x23x20cm
43x28x14.5cm
~17L
38x27x13cm
linear: 78cm 16L
35x25x16cm
linear: 76cm 13L
39x28x12cm
13L
30x25x13cm
linear: 68cm 8L
28x19x15cm
~8L
29x20x13cm
linear: 62cm 7L
20x15x8cm
linear: 43cm 2.5L