Hi, I did a Google and eBay search for a gas ring to run off domestic natural gas. It's required to heat a glue boiler in my workshop. There were none on eBay and very few to be found in UK via Google. These few were quite flimsy looking burners held in a pressed steel frame.
There is a picture of one in NZ which is really impressive. It's mainly cast iron and had 3 graduated concentric burner rings with pot stands cast in as part of the monolithic body. There are substantial feed pipes, at the end of which are 3 separate taps to operate each ring independently. This seemed to be set up for bottled gas but it may be convertible, or have a natural gas option. Here's a picture of it.