In this day and age, there´s plenty of sources about arms and armour.
A lot of them are available on the internet for free, and that´s great.
Here´s a list of the most common websites for primary (actual armour) and secondary (imagery and text) sources
These are just the main sites I use, but there´s more museums that offer their collection online.
Also, I´ve been trying to collect all the extant pieces of armour that survive from the XIVth century in this document, filled with data about the size of the pieces and when possible about their metallurgical composition and so on. Feel free to download it and share it with other enthusiasts.