Here are a couple of links...I have used the first one with good luck...
http://www.lolbait.com/
and
http://www.johnsonbaitplus.com/leeches.html
Also I have had better luck with large rather than jumbo...I dont know if the jumbos are closer to death since they are bigger or they want to spawn and die with I think leeches do...but I have been able to keep a couple of pounds of large leeches three or four months just by changing the water every couple of days...and keeping them cold in a garage fridge...
http://www.lolbait.com/
and
http://www.johnsonbaitplus.com/leeches.html
Also I have had better luck with large rather than jumbo...I dont know if the jumbos are closer to death since they are bigger or they want to spawn and die with I think leeches do...but I have been able to keep a couple of pounds of large leeches three or four months just by changing the water every couple of days...and keeping them cold in a garage fridge...