Cylinders are one of the few products that are still manufactured mostly in the UK. Most (all?) of the cylinder manufacturers do a custom build service. Do a drawing showing overall dimensions and where you want the tappings, and take it in to your local independent merchant. Get them to fax/scan the picture and send it off to the manufacturers for a quote. If you need it quickly, allow in your price for carriage. Its probably better to get them to make a cradle as well.
I don't know of anywhere that you can get one off the shelf.