Found these for you:
[ame=http://www.amazon.co.uk/Tales-Riverbank-VHS-Johnny-Morris/dp/B00004CUG9/ref=pd_sim_v_h__1]Tales of the Riverbank [VHS]: Johnny Morris, Peggy Miller, Josef Seckeresh, Dave Ellison, Paul Sutherland, Charles Fullman: Amazon.co.uk: Video[/ame]
[ame=http://www.amazon.co.uk/Further-Tales-Riverbank-Surprise-Stories/dp/B00004CN0N]Further Tales Of The Riverbank - A Nice Surprise And Other Stories [VHS] [1992]: Johnny Morris, Josef Seckeresh, Roy Billings, Dave Ellison, Gary Shoefield, Grainne Marmion, Paul Sutherland, Richard Hall, Simon Wright: Amazon.co.uk: Video[/ame]
[ame=http://www.amazon.co.uk/Further-Tales-Riverbank-Picnic-Stories/dp/B000068OUT/ref=pd_sim_v_h__2]Further Tales Of The Riverbank - The Picnic And Other Stories [VHS] [1992]: Johnny Morris, Josef Seckeresh, Roy Billings, Dave Ellison, Gary Shoefield, Grainne Marmion, Paul Sutherland, Richard Hall, Simon Wright: Amazon.co.uk: Video[/ame]
There doesn't appear to be a DVD collection as yet. Apart from the new version with Steve Coogan & Ardal O'Hanlon which has a very nice official site
http://www.talesoftheriverbank.co.uk/trailer
Hammy Hamster was a real childhood favourite of mine.