Does anyone know if they're making 48" Sinclair or Sinclair Avaition fakes?

If you mean Sinclair Aircraft, then yes, I believe they are. I know they have been reproducing them in the incorrect size of 42" for some time, but a recent Ebay listing says the one sold was a 48". I would certainly research and inspect a sign heavily before purchasing, which rings true for most signs now days.
Darin

The Ebay item I am referencing for a 48" is 182720933869