The Pinger chips are easily available for AMS members (for £5) but the hydrophone can be an expensive item to purchase.
A number of people have made their own hydrophones based on the Loughborough University model.
I include a reference to this to give you an idea but we have a lot more expertise within the AMS and I will post more in future. Generally when the AMS meets e.g Alfold, Barrow etc someone has a hydrophone so you only need the Pinger on your submarine but the more hydrophones out there the better!
The instructions for the very useful Loughborough unit can be found at:
The hydrophone itself:
(Note to Webmaster, I will also put this in the electronics section.