Where do people tend to order them from. Anywhere reccomended?

I use Sailboats.co.uk - good service, usually dispatched the same day if you order before lunch. Most of the big chandlers will have them.

Depends what and where for, I paid 1/3rd price for inflatable bags normally used as rollers, so long sausage shaped.

Support your local chandler!

I would support my local chandler but as I live around 15 miles from my boat and the nearest chandler is about 3/4 miles from the club it makes sense to shop online for me generally. By the time I have driven there etc.. will of spent more on fuel. Just my preference though for convenience.

A source of inflatable sausages is sought for a peculiar application, namely the reduction of the water-draught of a boat.  A friend lives on a boat in Cardiff but he wishes to sail to London in the quest for higher pay.  Travelling by sea is a distance of 520 nautical miles which would take ages and be quite dangerous.  As the man is a tightwad he proposes to use the sails to avoid burning diesel fuel but the wind may not be in the right direction!  The man refuses to pay for haulage by lorry and as the boat seems far heavier than its official weight I shall not be towing it again. (the deceased Commodore who was the boats previous owner had increased the ballast considerably)  During a rub-down of the hull the old waterline was discovered and it was about six inches lower than the present one!  Three marine surveys failed to spot this but the trailer tyres noticed the difference so it would appear that trailer tyres are smarter than some marine surveyors! 
 
My advice is to use the Kennet and Avon Canal as the savings on the cost of diesel fuel will pay the navigation fees several times over.  The boat is a Colvic Springtide 24 (long keel with bilge plates) and whilst it might transit the canal without any modifications a couple of large sausages might be extremely useful.