If you're too specific when searching for stuff you're likely to get no results. I don't recomend using the 'Usable by' search peramiter, when it comes to companions it looks for 'Usable by <Companion name>' on the armour, like the items you recieve specifically for your companion, and they're always bound to you.
start with a really broad search, just 'Armour' 'light/medium/heavy/adaptive'. leave the quality as 'Standard' since 'All' doesn't seem to work. See if anything comes up, if it does then start narrowing the search, perhaps by level, allow for at least 5 either side of where you're at, and go from there, searching by stat is usefull for more class specific items (I only use the main stat for that part (str, wis, cun, aim))... I don't recomend using the credit cap for searching, if you can't afford it you can't buy it, but you can at least see what's out there for what prices.
If you don't get anything with a broad search, then it's probably a bug...
as for quality, green are sufficient most of the time, i only narrow down the quality if there is an abundance of greens, blues or purples to choose from, which isn't often on my server ^^
sorry for the spelling xD Hope this helps