Complex sentence: The second series was an exclusive two-disc set on their website which has since been re-released on 3 September 2012, the third set was also a four disc set and it's available through the Network website.
Split into simpler sentences: The second series was an exclusive two-disc set on their website which has since been re-released on 3 September 2012. THe third set was also a four disc set and is available through the Network website.