The only two places I can think of that sell them are Machine Mart and our very own weldequip (who is available by private message on the forum). Both are very lovely, but weldequip will be easier to work with for support and spares.
Weldequip's prices are cheaper than Machine Mart in general apart from if you can buy on a vat free day at Machine Mart (every few months, different timing for different stores, and complicated enough for me to have never worked it out).
Brian, if you think you might run refillable gas cylinders then I'd suggest spending another £20 or so and getting the 160TE, it has a carrier on the back to fit the cylinder on.