This is copied from another website so if any of this info is inaccurate my apologies...
""Turbo" plug. technically speaking, their design offers an small advantage. A turbo plug is tapered and doesn't need a washer. It seals the combustion chamber nearly perfectly. Standard plugs with copper washers can allow leakage out of the engine's combustion chamber and possibly a slight loss of performance.
The tapered end on a turbo plug allows the combustion chamber to be smoother and less likely to disrupt the fuel/air mixture during combustion. There isn't any concern with the thickness or reusability of glow-plug gaskets either.
With that said, IMO, we would not be able to notice the ever so slight performance enhancing benefits however, it is what it is."
As for where to buy them you can get them any place that sells regular glow plugs....LHS, Amain, Tower, ebay etc.