Let's try that again. There are 3 different common current sources for these tanks.
Source 1, looks to be older production indian stuff. Can find this either raw, painted, etc... Bottom is made of multiple pieces. Not leak tested, some people have had bad luck on here, actually. $200 for a raw one.
http://www.ebay.com/itm/NEW-NORTON-COMM ... 7b&vxp=mtr
Source 2, looks to be made with a one piece bottom stamping also indian made, with welded in bungs and a seam. Leak tested. $250 for a raw one.
http://www.ebay.com/itm/Norton-Commando ... 35d8a202d7
Source 3, made by EMGO (somewhere in the far east, not sure), made with a one piece bottom stamping, clean welded in bungs and a seam. Leak tested. $450 for a raw one.
http://www.ebay.com/itm/NORTON-COMMANDO ... 30&vxp=mtr
There are also a few makers of alloy tanks in India as well as boutique builders, but that's probably not in the interest of an average tank buyer in terms of price or timeframe.
You can get source 1 from a bunch of ebay vendors. There are reviews and pictures on this forum of tanks from source 1. They're made in multiple places and with different production runs so some people had great luck others had terrible luck. Source 2 appears to be only from commando specialists. Source 3 is available from baxter, bonneville shop, old-britts, CNW, etc... It costs a lot to tool up stampings for tanks, so keep in mind the number of people knocking out roadster tanks is VERY few so it's easy to see where they come from.
To reiterate, you're probably fine with one from source 2 OR source 3 as both are leak tested.