Wikimedia Commons has two images of Atilla the Hun from the Chronicon Pictum, dated around 1360. Is there anything (coin, portrait, bust, statue) older than that?
Not really. Portraiture as an art was having a bad couple of centuries in Attila's time. Whatever we know of Attila's looks comes from written descriptions that differ significantly from one another and are oftentimes embellished. It stands to reason that he was short, like most of the great conquerors. Beyond that, it's anybody's guess.
I'm not sure how useful this is to you, but there is a second-hand contemporaneous description of what Atilla looked like.
The original source is Priscus, who visited Atilla's court in 449 as a diplomat. There are no originals of his description known, but there are later authors who make reference to it. Here's what Jordanes said in the 6th Century, sourcing Priscus:
He was haughty in his walk, rolling his eyes hither and thither, so that the power of his proud spirit appeared in the movement of his body. He was indeed a lover of war, yet restrained in action, mighty in counsel, gracious to suppliants and lenient to those who were once received into his protection. Short of stature, with a broad chest and a large head; his eyes were small, his beard thin and sprinkled with grey; and he had a flat nose and tanned skin, showing evidence of his origin
If you want an actual description of the guy, this is probably the best we have. I'm guessing "showing evidence of his origin" is somewhat coded language for something, but other than "he's not ethnically one of us", its tough to say what that something was at this remove.