Got mine from Potomac German Auto in Frederick MD.
They have another store in St Augustine FL.
http://www.mbpartsonline.com/
They have an on-line search function for parts but its not totally representative of what they have in stock. If you call they will be able to tell you exactly what's in stock.
Should be able to ship a differential to you by UPS, but its heavy. It works best though to be able to look over the part you're about to buy.
Ken300D