You're basically looking for uke x uke with neither of them knowing the other is the same. I can think of a couple that both of them know the other is uke, like http://www.mangago.me/read-manga/hi_manyuaru_ren_ai/ , but I don't know any off the top of my head where they don't know ahead of time.
I'm not sure if it what you're looking for.
This one it's a straight uke story, I love this story (≧∀≦)they get to that misunderstanding at one point.
http://www.mangago.me/read-manga/soredemo_yasashii_koi_o_suru/
სამწუხაროდ ვერ ვიხსენებ მზგავს ვერაფერს :// მაგრამ უბრალოდ პრივეტ
Is here any manga where guy A thinks guy B is seme and guy B is thinking guy A is seme and waits to be fucked by him...while A thinks the same....... sorry for horrible English and hope someone will understand what I mean....