1. You have to
2. You have to have enough singers. I remember listening to a huge choir sing a song my smaller choir had struggled with. I wondered how they sang it so well. A very experienced musician said, "If you make enough noise and have enough people in each part, no one will ever hear you sing a wrong note. It will be drowned out and become part of the whole.
If however, you have a smaller group, then every note is heard so be careful that you have enough voices to sing them. We are a group of less than 20 and we are NOT going to sing in 8 parts. We sing SATB or SAB occasionally splitting for a short time for a descant or obligato.
3. Get your singers(musical director) on board. Sometimes it isn't so much the notes of the music but the overall effect that will sell it. We have worked on some arrangements that are tricky in timing. It takes some doing to get the parts just right. But the choir and director are willing to do just that because they know that the result is going to be worth it. Sell the result by listening to good recordings of that arrangement and everyone will be willing to make it happen.
4. If it doesn't work, let it die! The piece is well known; it has the right part structure; everyone can reach all the notes without struggle. Yes, all the elements are in place. BUT it just isn't coming together. STOP. Put it away. Maybe forever or maybe just for a while. We have gone back to a piece that seemed impossible and there it is surprising us all. Some we just let die.
5. So how do I find the music? Borrow something from another choir that you enjoyed listening to. Try a couple suggested by others. In this day of social media, you can ask choirs of your type all over the world for help. Keep trying something a little different. Most will work, some won't. So learn and move on. Just keep singing.