Well, It's not a full set of armor, I'm just a peasant and can't afford it, but you can get the helmet, the chainmail coif and the tunic for a fair price on Amazon (You should have a strong neck though, it's all quite heavy and not easy to wear).
https://www.amazon.com/SZCO-Supplies-Brass-Crusader-Helmet/dp/B007XP1ECS Here's the helmet, there's a suggestion for the rest of the stuff but you might wanna spend some time looking for good prices.
Good luck crusading out there my friend!
kult of Athena is a good place to buy expensive and well made ones but you can get one on amazon for a good price but not as good.