Google "dock Xperia SP" and I found a product named M35H sold around 10€ by various web dealers.
Despite the absence of choice, I recommend this product.
- Stable, Non-slip feet
- Rear micro USB socket
- Charge and data sync
Only quality ABS used does not reach OEM, but it works fine anyway!
I made a little video for you...
About dealer, this thread is a review product and I would not advertising.
Make your own choice!