Can anyone help me find the perfect ring?

Double check that she likes whatever you get. See many posts on unhappy brides and their rings.

My fiance got my ring from a site called Allurez and he custom designed it (it was a ring I saw on Pinterest and he found it!).

There are some with a similar styles and you can choose rose gold. I'm not sure if that helps at all but if not, there are definitely other custom ring sites out there. Best of luck!

Since they make their own pieces in house have you contacted them to see if they could make the piece custom for you with the different cut center stone?

I just looked JamesAllen.com and I think they have styles similar to what you are looking for. You pick the stone, the setting, and the type of gold. That is where we got my ring and I absolutely LOVE LOVE it. They have a 30 day money back policy if she doesn't like it, and a lifetime warranty.

I definitely second the James Allen comment. That's where my FH got mine and I love it.

Verragio is a custom ring site that you visit the jeweler and they facilitate the process for you. You can go rose gold, white gold. 18k yellow or plat with that site

Hey! My fiancé bought my ring from Catbird, and I love it! Have you and your FS visited the store? If you haven't, already, you might get a better feel by seeing the ring and other rings in person.

Digby and Iona has some similar styles and I read that the designer does custom work. You have to make an appointment to visit his Brooklyn studio.

http://digbyandiona.com/

Is she dead set on having you propose with THE ring? If not, you could always propose with a simple solitaire in the cut she likes, then custom design a new setting together. That takes the pressure off of you to have the perfect ring from the get go.

My DH custom made mine. He found a jeweler that did them and he said it was a very easy process and he designed the ring from scratch. It turned out perfect.

My fiancé had one designed for me based on a picture I pinned on Pinterest. Mine is rose gold with a regular round diamond.

I agree with pp about asking if they can custom design for you. FH and I custom designed my engagement ring in store together and did the same with my wedding band. They're rarely giving you a ring off the shelf so it's usually not too big of an issue to ask for tweaks here and there