The best store (in my opinion) for purchasing armor in the SCA is http://www.windrosearmoury.com/zc/ I am best friends with the armorer and they can and will make any style and era fighting kit that you need. They can be moderately expensive but if you check the website then you'll see why.

I've been fighting in the SCA for 9 years now and trust me the better armor you get the better it is for you. Just walking out on the field wearing really cool armor makes a world of difference in not only your own fighting style, but how others will react to you. For example if you square off against someone in a $60 dollar helmet and a blue plastic bucket as a chestplate, odds are that he's pretty new and you probably don't need to fear him as much. On the other side, if you are wearing a awesome looking suit of armor you can actually scare people by just acting the part, even if you don't know what you're doing. It's fun.

Good luck!