Q: ITunes Pass Retailers?

I think you are asking how to add funds to an iTunes Gift Card.

Once the gift card has been used, it is not possible to add funds to it.

However, you may purchase additional iTunes Gift Cards online.

Send iTunes Gifts via email - Apple Support

UPDATE: I have now read the iTunes Pass article you attached at the top.  The way to add money to iTunes Pass is to purchase and redeem iTunes Gift Cards as shown above.  Once that credit balance appears in your Apple ID, you can transfer it to a Pass as described in the article you attached above.  Here is the appropriate section:

So you do not have to visit any retailer at all!  You can do the whole process online.