Asked politely, are you really sure you are dealing with 15mm bore gas hoses with push on nozzles?
Getting a 15 mm gas valve is easy, even Screwfix do them, push on 15 mm nozzles though would be challenging, if not also worrying.
Since posting I've found a suitable 3 way splitter which is ideal Just want to cut off the gas to either BBQ OR gas ring or, if necessary, have both operating.
You don't tell us what gas you are using, but I will assume its Butane or Propane, in which case the pie should not be rubber as these gasses will dissolve it.
If you are not fully aware of what is required to safely handle LPG's please consult a qualified professional and heed their advice for you and your family's safety.