An absolute gem. Currently available (all 3 series and Christmas Special) on BBC iPlayer at:
https://www.bbc.co.uk/iplayer/episodes/b06l51nr/detectorists
Am going to upgrade my copies too.
Apparently it is on Amazon Prime, just not in the U.S., so if someone overseas could grab that and put it on Mega.nz that'd be great:https://www.amazon.com/Jamies-Return-School-Dinners-Hornby/dp/B076CRRY76
No secret. Found it here https://idope.se/
Good site for finding older stuff.
Quite often find that although it says SE=0 there is indeed a seeder; so if find no luck with SE>0 torrents then try the torrents for S=0 also.
Hope this helps.