You can get an E flat Lee Oskar harmonica, but the shop you go to may have to order one. It's not a key that most shops would stock. Or you could try the capo up another fret and play the E harmonica. That'll save you about £20! The change in pitch shouldn't be too critical for your voice. If you're playing with other people with fixed pitch instruments, like fiddles and accordians, they would probably prefer the key of D.
The point that Mark raises only really applies to blues and blues related music. You would know if you were playing that style.