Hello sir/madam, my name is George,
You are correct in saying that the burner parts are now obsolete and not available.
The burner in your grill can however, certainly be cleaned and serviced, providing it is not too far gone. To do this you will need to aquire the services of an appliance engineer who has experience as he will need to remove the burner from the system to clean it. This is best done by a Gas Safe Appliance Engineer.