I am a soprano/trumpet player, but I have recently acquired an interest in mellophone. Does one have to have to buy a mouthpiece just for mellophone, or can they have a french horn mouthpiece to play a mellophone.

I know french horn mouth pieces are similar to trumpets/cornets/sopranos, but which mouth piece for french horn or mellophone should I get to best simulate the mouth piece of a (5C) trumpet.

I am also a trumpet player and marched mellophone. We used the Benge mello 6. They also make a 6V. I think most corps may still use this mouthpiece, but I heard that some of the new F mellophones may need a different size shank. That's just a way for a company to make people use their mouthpiece because its the only one that will fit their horns. Still, the Benge 6 is the standard and you should do well with it. I would stay away from a French horn mouthpiece unless you're playing a concert French horn.

I use a King Mello 6, but if you are just starting out, just use your 5C, it should fit into the mellophone

Or get a French horn mouthpiece and an adapter. It may cost a little more but the sound quality is much better. I play on a shilke 30 and my tone is way prettier and darker than a melo mouthpiece.