Ya, they are very rare in the show, in my story alone there about 8 in total so far that been in my story, I avoided adding alicorns and if any alicorns I would encounter would be female(Unless something I could explain) as there hasn't been any mention of a Male Alicorn in the series so far.
Well at least its consistent with the show if there is many Pegasi OCs, Its more believe-able if they where existing in the universe than a over amount of Alicorns.