Standard diatonics (aka Richter or blues harmonica) typically have only 10-16 holes across.
A blues harmonica is primarily laid out to repeatedly create a single major chord on the blow notes, I-III-V-VIII, do mi so do, however the upper octave is arranged to provide an entire major scale when combining blow and draw notes by including alternative draw notes.
Once you have more holes across than that though, you are likely looking at a different scale arrangement as well. The possibilities include:
A repeated major chord (no complete major scale), with a range of more octaves.
A different scale altogether, or at least more recurring notes than just the major chord.
No draw notes at all, and the extra blow holes are interspersed to provide those missing notes instead. That being the case, it's more likely to be a chromatic harmonica in the first place.
The example I provide below of a tremolo harmonica in which blow and draw holes alternate.
I have a Paloma Harmonica with the following charts included for 21, 23, or 24 holes:
[21] redo^ fa mi^ laso^ ti do^ remi^ fa so^ lado^ ti mi^ reso^ fa do^ la`
[23] redo^ fa mi^ laso^ ti do^ remi^ fa so^ lado^ ti mi^ reso^ fa do^ lami^ ti
[24] so^ redo^ fa mi^ laso^ ti do^ remi^ fa so^ lado^ ti mi^ reso^ fa do^ lami^ ti
Blows are indicated as ^, draws are indicated as `.
They add a mi ti at the end for 23 holes, and a so at the beginning for 24 holes.
This is a strange harmonica though. Each hole, by which they mean a vertical stack of two holes, alternates as a blow or draw hole. This is why the harmonica has twice as many holes.
To use the format of Dr. Mayhem's answer (which doesn't really fit the harmonica), it would look like this:
G^ DC^ F E^ AG^ B C^ DE^ F G^ AC^ ti E^ DG^ F C^ AE^ B
(since it's in the key of C)
Or like this if the blow/draw holes were synonymous instead of alternating:
Blow G C E G C E G C E G C E
Draw D F A B D F A B D F A B
I wouldn't recommend such a harmonica for serious musicianship unless the tremolo is your priority over expedience, chords, and bending. It could be useful if you wish to avoid playing more than one note at a time though.