Euron found the breast plate stretcher (spoilers TWOW) In the TWOW chapter the forsaken Euron is seen by Aeron wearing armour made from valyrian steel which he got on his trip to valyria. 

One thing this has made me wonder is, how did Euron got armor his size and I came to three conclusion:

1- Euron got really lucky

2- There is a butt load of valyrian steel armor still there, but if there is so much valyrian steel there why was it expensive to buy even when valyria was at its peek

3- Euron found the breastplate stretcher