Are you looking for leaks in a natural gas line or propane?
cuz' I use a really cheap and effective product called snoop. It is a soap solution in a squeeze bottle and you dribble a little on any fittings and a leak will bubble. I found this quickly on google
http://www.scottecatalog.com/equipsp...8?OpenDocument and you should be able to get it at any hardware store or BBQ repair shop.