Hi briatkin,
welcome to Club VAIO Questions & Answers Forum..:smileyhappy:
You may find a Sony battery for your Vaio by searching via Google, however be aware that some being sold are compatible models..
However you should be able to purchase an official Sony battery for your VGN-SZ4MN from Sony support or possibly via one of Sony Service Partners, you can the contact details by either clicking Support at the top of this page or use the following link:Vaio support
Under Log-in option 2: Select your VAIO model, next to Select Model Category - Select your model from the drop down list, in your case VGN SZ.
Then next to Select Model - select SZ4MN
Then click Log-In
Once logged select Get In Touch and click on the Out of Warranty tab..
