Unless you just happen to live next to a great music store in Utah, it can be hard to find choral music, especially LDS choral music. While some local Deseret/LDS Book Stores carry some choral music, the selection is usually slim at best. You can check your local music store for non-LDS choral selections (i.e. John Rutter and the like), but I like to order choral music online or over the phone. Some of the best places I have found for ordering music are:
Day Murray Music (www.daymurraymusic.com, 801-266-3537)
If you ever go to Salt Lake City, Day Murray music is the mecca of LDS choral music: they have a huge, unparallelled selection. I could (and do, when I go to Utah) browse there for hours. If you are not within driving range of Salt Lake City, they are easily reachable via telephone or internet. They tend to have a lot of music in stock and get it shipped to you very quickly. They are one of the best places for ordering LDS music, and they carry just about everything else as well. They also have a very knowledgeable staff and lists of recommended music if you need some ideas to get you going.
JW Pepper (www.jwpepper.com, 1-800-345-6296)
The world's largest sheet music retailer.
SheetMusicPlus.com (www.sheetmusicplus.com)
There is often a bit of lead time required, but they have very inexpensive shipping and a fairly good selection. There is a usually a minimum order of 6 copies of choral music.
Jackman Music (www.jackmanmusic.com, 1-800-950-1900)
A good source for LDS music. They only carry LDS music, but they have a great selection and are very fast. If I place an order on Monday or Tuesday it usually gets to me by the end of the week. You can order via phone or website. Shipping charges are very reasonable: they usually only charge you the actual shipping cost.
Note: I have no official affilliation with these companies. I just have had good experiences ordering from them. If you know of any other good sources, email me and I will add them to my list.