Sonic Adventure 2 Battle can sometimes be found in the used games section of Gamespot for really cheap. The original DC version is no longer for sale. You can probably find both versions on eBay.I bought the Sonic Adventure 2 battle version on eBay this January, the Dreamcast version was there too, but it was a while ago.
Battle
You can search on the internet to find cursors. OR With Sonic Adventure DX Director's Cut, on the first disc on the PC version of the game, on the special section there was the option to choose from a selection of Sonic characters from the game to be your mouse cursor.
They are near the master emerald shrine.
You first see her at the beginning of the game. On South Island, go to marine's house. you should find her there.
youtube
it doesn't exist
Ebay
yes you can find it in many levels
you can find them in Pumpkin hill
Aquatic Mine and Iron Gate
I believe sonic and tails can get bears in final rush for sonic for tails im not sure.
Actually there is a way to hack sonic adventure 2 battle and play as super sonic in normal levels just look around the internet and im sure you will find your answer.
Find a fish and use final slash on it.
There are goggles but their not called goggles, they are called sunglasses.
Find a mystic melody (usually in mission 3) and you can use it.
buy it preowned at game stop for around 8 dollars.