You are referring to the
terracotta ones I take it? There are a nember in the
fakes gallery here. There are some genuine examples, for example the excavated ones fro Palmyra published in
Numismatic Chronicle in the 1990s , or early 2000s.
There is a general feeling that the highly die linked examples on the market just over 20 years ago may well be largely false. However, how to tell genuine ones amongst all those I don't know.
Regards,
Mauseus