Where can I buy a replacement hard drive?

Hello everybody.

I have an iPod classic 7th gen with 160gb, but it needs a new hard drive. (it has 16376 reallocs, yet 0 pending sectors)

Now is my question which hard drive to buy?

Here on the ifixit website the hard drive is out of stock, and when I look on ebay, there are a lot of different types (with a lot of different prices too).

I'm not the most technical person, yet replacing the drive won't be a problem for me, but choosing the right one is... (I don't have any knowledge about the specifications etc.)

Thank you for helping.