I want to add new avatars and clickable artworks, where do I send them? 

For avatars got yo your profile page (compass icon-profile) and select "upload avatar" bottom of the page.

 

Other artwork you need a GM to work for you.

As a non-A25 realm-shaper myself, I usually work in tandem with various A25 realm-shapers when it comes to scene, clickables and creature artwork implementations. If you want to submit a concept art or are interested in being involved, you can show off your PoC/demo via the forum gallery, the MD Artworks subforum, or by talking directly with one of the GM's/A25 members.

For avatars, typically you just upload them to the profile section of the game located on the left hand corner of the page. The artwork needs to meet certain specifications, you can find it HERE.