My understanding is that there's an order form on Pride Online, but I won't swear to it. I never realized it before GreekChat, but it seems that certain chapters have a tradition of everyone ordering the same pin, or otherwise restricting what type of pin you can order. But one of the beauties of Alpha Delta Pi is that we can each order a pin that suits us - yet that Black Diamond is what binds us together as sisters.
Among the different types are white gold or yellow gold; regular size or "miniature" (I could never see the difference!); plain border, chased border, pearl, diamond, opal, alternating pearls & jewels border or other jeweled border; jeweled points, etc, etc. And then, the same for the guard.
Another place you can occasionally find pins is on ebay. I bought a pin as a ring there (pearl border, ruby points), but one that I thought was simply stunning was an art deco type: plain border with pearl points!
I was fortunate in that my parents bought me "the pin of my choice", and also bought one off of a sister who was selling hers. It's nice to have a choice.
Hope you find the pin of your dreams!!