A classical accordion or bayanist playing 4+16 register or a 4+8+16 combination can imitate some organ like sounds.
Western free reed music instruments dont really need pipes to sound out loud. Some tubes or pipes can help affecting sound or volume, but in (Western) metal free reed music instruments, the effect is limited.
The beauty of western free reed music instruments like the accordion, concertina, harmonium, melodica, harmonica, ... is you dont need the pipes or tube resonators.
You can make the music instrument in a very compact way, and at lowcost.
The history and evolution of reed organ and harmonium making shows the pipes were left out. Because they had only marginal effect on sound production.
https://en.wikipedia.org/wiki/Pump_organ
Expensive harmoniums were often built to resemble pipe organs, with ranks of fake pipes attached to the top of the instrument
Asian free reed instruments do have pipes and tubes, and they have some limited influence on sound, but the revolution of free reed music instruments in the 1770-1830 period was that pipes or tubes are unnecessary in free reed music instruments.
In the sheng, the pipes traditionally are a poetic representation of the closed wings of a bird
The shêng was formed to imitate the shape of the tail of the Phoenix bird — fêng-huang — and the length of the pipes has no effect on the pitch; the shape is simply decorative. , a quote from this page:
http://www.ksanti.net/free-reed/history/sheng.html
It was the revolution by Friedrich August Reichstein (1794-1869) and Charles Wheatstone (1802-1875) around 1828-1829 to make mini free reed instruments without pipes or resonators, such as new sheng (Neu-Tschiang) or symphonium, much more compact than a large sheng, without the pipes.
The Asian sheng only keeps the pipes out of tradition, there is no reason to keep those pipes, only for some marginal sound effects. It does have some influence on the sound, but in a limited way.
The sound of the Russian Timbre group ensemble is much more influenced by specially shaped tone chambers and the shape and material of the reeds. There are no pipes inside.
Melodicas dont have pipes, idem for the harmonicas. Harmonicas with trumpet horns have existed, but more as collectors items.
Some Steirisch Harmonika accordions have on the bass side trumpet formed small horns or bells or whatever you might call this, but this is mere tradition and decoration.
If you want to experiment with variations in sound, loudness, rather look at the material, size, thickness and hardness of the reeds, and also the size of the bellows, the air pressure, the number of voices in a register.
If you like the sound of an organ, look for YT videos with organ pieces arranged for classical accordion or bayan. Many listeners often confuse classical accordion with an organ, when hearing a hidden accordionist/bayanist busking with Bach pieces.