Please bear in mind that composing and/or converting songs into MML format takes an incredible amount of patience and dedication. Thus, people generally do not appreciate giving out free codes to others who are just going to use them without crediting the composer. If you have a friend who composes songs or know of somebody who takes requests, you could try to kindly ask if they'd write the song for you. Some composers charge their services, so be prepared to pay a fee.
I suggest taking this request to
Tireku's official request thread, which is stickied in this forum for good reason. There are also a couple of websites where people post codes free for the taking, so you should google those as well. Here are a couple you could start off with:
Mabinogi Music Score Library & Request | Free to Play @ Curse.com
Nexon Forums - music scrolls here free songs for mabinogi just copy and paste onto your scrolls