I have created a wish list but can't find a BUY button.

You should see the price of the item to the right of the listing. Click on the Price, and it will prompt you for your Apple ID password. At the bottom of the sign on window you will see the "Buy" option:

Cheers,

GB

Read this:

iTunes Store: How to use Wish List

moroak wrote:

I have a Wish List but can't do anything with it. There is no buy button to be seen.

You may remember that in older versions of iTunes there was a single button to buy the entire Wish List at once. That feature was removed.

Now, the only way is to buy the items one at a time as described by Gail.