Como dizer "Mosca branca" em inglês

My suggestion:

Finding an intelligent and beautiful woman to like you the way you are is like finding rocking horse sh*t.

Finding these tennis shoes in Brazli is like finding rocking horse sh*t.

Bye!

Expressões similares:

To be a real find (algo útil e de qualidade achado por acaso)
To be hard to come by (algo difícil de encontrar)
To be as rare as they come (algo muito raro)
To be as rare as hen's teeth (algo muito raro)
To be a keeper (parceiro com todos os atributos desejados)

Exemplos:

"These sneakers are as rare as hen's teeth in Brazil".

"A good, honest car mechanic can be hard to come by these days".

"Your girlfriend is a real keeper."

"A good hotel this cheap is a real find".

A hard thing to find/ A real gem

It's a hard thing to find the right actors who will play it straight; again, not indicating that they are doing anything funny but at the same time doing the most ridiculous things.
The Guardian

Sako has been a real gem since signing for Wolves in 2012, scoring 30 times in his 99 matches.
Daily Mail

Achar uma mulher linda,inteligente que goste de você do jeito que você é,isso é mosca branca.
It's a real gem finding a pretty and smart woman who likes you the way you are.

É mosca branca você conseguir achar esse tênis no Brasil.
It's a hard thing to find these trainers in Brazil.

To the sneakers, maybe I would say "Wow! A tennis shoes like this with this price, is a hard-to-find bargain in Brazil, a never seen (before) bargain indeed! (it´s not normal in Brazil!/it´s not everyday that we see a bargain like this in Brazil!)

There are other ways, of course.

About peculiar or unusual things...also not usually found.

Also: "as rare as white flies" (hard to find/hard to get.)

http://www.autoguide.com/auto-news/2012 ... r-ceo.html
Muscle cars like the Hemi-powered Dodge Challenger, he says, will become “as rare as white flies,” ... And, as many will point out, the V8 continues to be found under the hood of quite a few cars.

In Englis is common the saying "a rare bird" to strange, maverick or to people that aren´t very bound to general standards or tastes.

In the Spanish comunity in America you could hear/read
Eres mas rara que un perro verde. (You are stranger than a green dog.)

Ref. books.google