They are really rare, because they were custom made by a dude called Andy Kein? from the UK (he's pretty famous on the UK skyline forums), he designed a GTS and GTT badge and produced it from stainless steel.
I emailed him on ebay 2 weeks ago about a GTT badge and he said he will be getting some made soon. They go for about $20-30.
Apart from his, I haven't seen anyone selling or making it