Hope this migth be of some help:

Great site for finding measurements.
http://www.barenecessities.com/feature.aspx?pagename=bra-fit-checklist&cm_re=Fit_Sizing-_-2.1-_-CheckFit

Measurement is super important. Having a bra-fitting to find my measurements changed the life of my boobs dramatically to the better! But if a bra-fitting is out of the question, there are instructions of how to do it yourself. Like the link above. I am a f/g-cup, and I have a slender waist, so finding a bra with big cups and a band-width that fit me, was really hard. I was always wearing bands that were never where they were supposed to be, or the cup was wrong and made me look like I had a double set of boobs. Bands were always digging into either my back or my shoulders or both, riding up and making the absolute worst of my "back-fat"... could go on forever... Getting the rigth measurements solved those issues. (I kid you not!It did!)
And for the maddening process of finding a bra/store that has that band-width; as a starting-point here is a list of where to get bras with wider band sizes for small/average cup-sizes:
Where to buy big bands with small cups - Venusian*Glow

When in doubt, I recommend calling a store to find out if they have your measurements before wasting time and energy by going there, only to discover that they don't have a f...ing clue what you are talking about... ( I have done this several times, and saved myself the time and the money to travel, as well as the hassle of not finding what I came for). By calling them you have made them realize that they just lost a customer by not having a better selection. Even better; write en e-mail to customer support. I worked as a store-manager for a while, and I can tell you that one really smarts.
I know people also order directly from the maker when they find the rigth bra. The brands themselves have web-pages with their own customer-support and they probably would have a lot of good advise as well. And be able to point you in the direction of a store that carries the bras that would fit you.

I thought that my dream of finding a beautiful, sexy bra was not going to happen, and that I would have to go through my intimate moments wearing granny-bras. Thankfully I was wrong. I just had to do a lot of research first... and have a proper bra-fitting...