How do I get more items from the wardrobe?

Depending on what you want from the wardrobe there are many ways to get things.

Firstly, to get stuff like new eyes/hair/smiles/ears etc you can either get by using up AP (which is earned through battles) or with Diamonds which is the currency gotten by real life money (tho if you don't want to spend real money to get it there are other ways to).

To find out how much AP you have you can either look in the wardrobe below all the items or you can look in your boxes that show up below your avi

You can also get clothing from AP and Diamonds as well.

As for the Items section there are again many ways to get the stuff in here, tho most of them are in time restrictions (aka you would have to hunt them down from users that were around when they came out).

Custom Item - These are Items one gets by customizing Monthly Avatar Items.
Avatar Shop Item - These are Items you can only get from the Diamond shop.
Exploration Item - These are items that can be dropped by Enemies/bosses/companions in the exploration zone.
Merchant Item - These are items you can get at any of the merchant stalls in the cities/villages.
Forum Game Item - These are items that are handed out as prizes for participating/winning forum games hosted by the Admins.
Holiday Event Item - These are items that are dropped/found/sold etc during a festival or holiday occasion.
Monthly Avatar Item - These are items that are on sale for Diamonds during each month. They last in store for said month and after that month is done they do not come back into circulation on the site.

(Slight addition on Willow's awesome answer..)

Monthly Avatar Item - These are items that are on sale for Diamonds during each month. They last in store for said month and after that month is done they do not come back into circulation on the site. All Monthly Avatar items are sold for a limited time during the Black Friday sale in late November.

...300k AP O.O

And some Festival items will also be custom c:

IKR but there is nothing to do with it, even if I went and bought everything from the wardrobe I would be left with about 200k :p

(Just think what older players like Pirate and Draco have stored away...)