there was a scene from Escape From Catrina where baby surprise was an alicorn it could have been an image glitch or a fake horn but she appears to have a horn in that episode
http://derpynews.com/wp-content/uploads/2013/05/surprise-alicorn2.png
That was nothing more than an animation mistake. Animated shows in the 80s were rife with them.
Here's a page detailing (a fraction of) these in the G1 Transformers cartoon, including a link to a gallery on the top right.
Alicorns/unipegs/pegacorns as it pertains to Official My Little Pony Canon
(TM) were non-existent until G4 came along. There is one, single exception, but one that is also kind of... Should I say, meaningless, in the long run.
In the "Up, Up, and Away" episode of My Little Pony Tales, the Glow 'n Show ponies make an appearance, but they're all given wings to up their "strange and magical" appearance. ...Including Dazzleglow, who, being a unicorn originally, gets unwittingly turned into an, you guessed it, alicorn/unipeg/pegacorn.
Here's a picture (careful, it's HUGE).
In my opinion, the omission of winged unicorns from the line makes perfect sense, since it would be kind of overpowered compared to any of the other types of ponies. Fiction-wise, an alicorn/unipeg/pegacorn is, or should be kind of a big deal and rare, otherwise you end up in Mary Sue territory. And that's exactly why G4 chose to use them in the way they did.