Useful link here I used when buying mine (link). Gives the part numbers for both tubed and tubless and also shows you a side by side comparison so you can tell from photos whether it is a tubed or tubless rim.
As long as you are willing to travel your best bet would be ebay. Having bought two tubed sets of 4 wheels and tyres and swapping the tyres around myself, by the time I had sold the two spares I ended up with 6 HD tubed rims with tubes and very good xzl tyres for £50.
Plenty of people do not know what they are and just advertise them as land rover steel wheels so worth trawling through those. Any that are advertised as wolf rather the HD or painted in nato green will also be more expensive despite being the same wheel.