Just Who are the Thomas Manufactuers

Plarail is the name of TOMY's (main) toy train system as a whole, not a manufacturer. Oddly, it seems TOMY never actually used it outside East Asia; not even on non-Thomas releases. Both Tomica World (late '90s-early 2000s) and Tomica Hypercity (early 2010s) were European-American-Australian releases of Plarail. Tomica is also a brand of plastic/die-cast vehicles with their own road parts and accessories, which were also included with Plarail trains in Tomica Hypercity playsets.

Was Hit Toys  the manufacturer of the Trackmaster Thomas line in both US and UK?

Was any Thomas line products avaliable in the US in 1992?  If so, how manufactuered them?

For the first question, yes. Take note TOMY still has the Thomas rights in Europe at the time, so the Trackmaster toys from Europe wear the TOMY logo until the toy range was bought by MATTEL in late 2009.

For the second question, the short answer is no. Before 1997 or so, there used to exist a range called TOMY Trains which featured the dark blue track system.