Harry would never have seen Salazar Slytherin’s wand.
Salazar Slytherin’s wand is one rare magical object that Harry wouldn’t have interacted with. We know from the JKR Pottermore writing on Ilvermorny that Salazar Slytherin’s wand had been passed down for centuries to members of his family, and that his wand had a basilisk horn core (which would be a quite rare wand core since basilisks were rare and dangerous creatures).
In all the years that she had lived with it, Isolt had never known that she held in her hand the wand of Salazar Slytherin, one of the founders of Hogwarts, and that it contained a fragment of a magical snake’s horn: in this case, a Basilisk. The wand had been taught by its creator to ‘sleep’ when so instructed, and this secret had been handed down through the centuries to each member of Slytherin’s family who possessed it.
- Ilvermorny School of Witchcraft and Wizardry (Pottermore)
During what would be sometime in the seventeenth century (Isolt was born in 1603 and Ilvermorny was founded in the seventeenth century), Isolt buried this wand outside the grounds of Ilvermorny.
Slytherin’s wand remained inactive following Gormlaith’s command in Parseltongue. Isolt could not speak the language, but, in any case, she no longer wanted to touch the wand that was the last relic of her unhappy childhood. She and James buried it outside the grounds.
- Ilvermorny School of Witchcraft and Wizardry (Pottermore)
It likely didn’t stay as a wand underground - a tree grew from where it was buried, and the implication seems to be that the wand itself somehow sprouted into this unusual tree.
Within a year an unknown species of snakewood tree had grown out of the earth on the spot where the wand was buried. It resisted all attempts to prune or kill it, but after several years the leaves were found to contain powerful medicinal properties.
- Ilvermorny School of Witchcraft and Wizardry (Pottermore)
Since this wand had been buried and became a tree hundreds of years before Harry was born, (and of course we never see Harry have anything to do with it in the seven books), it’s a reasonable conclusion that Harry would have never have seen or interacted with Salazar Slytherin’s wand. By the time he was born, it’s been a tree for centuries - the wand no longer exists as a wand.