I was looking through the various items that I have access to on DnD Beyond for my character. I noticed Pride Silk and it talks about how 4lbs of it can make a Pride Silk Outfit. A Pride Silk Outfit grants 11+Dex for your armor class instead of the standard 10+Dex. However, I don't have access to a Pride Silk Outfit. My question is that am I missing a sourcebook to get it (if so which one)? Or is it a bug at the moment? Or is Pride Silk Outfit not an item that shows up because it was set up that way?

Another question (if it isn't set up to not show up); is Pride Silk Outfit considered "armor" (because, from research, it is considered light armor and requires proficiency) or "other item" (because it is considered clothes)?

I guess I could easily fix this by using leather armor where I change the name, the weight, and the cost to that of "Pride Silk Outfit". 

So. I found out Pride Silk Outfit is from Guide to Wildmount. But I don't see it being offered as an item when I look through what it offers. Is it hidden behind something I can't see?
Also found out that it is not considered armor by a Twitter post by the one and only Jeremy Crawford.

It's not armour - it's clothing - but because of a limitation with DNDBeyond it's listed as light. Because it's listed as light - it requires light armour proficiency. If you're a wizard (for example) with no armour proficiencies and you search for it in equipment - you will likely have the Proficient checkbox ticked - if so - it will be filtered out.

Also make sure you have Critical Role Content turned on (red/right) in the Home section of the character builder.

Apperantly on DND Beyond its listed under armor. But it's considered clothing 

Like I said - that's a limitation of the DNDBeyond system. They had no way of making clothing equipable like armour and also give AC when they implemented it. They probably still don't - or it's just a very low priority to fix it. Either way - it's not going to get fixed any time soon.