Jim, About 2 years ago the EPA put restrictions on importing these trucks. The motors must be EPA certified to insure they meet the US emission requirements before they can be imported.
I know that Suzuki, Mitsubishi, Nissan, and Daihatsu mini trucks are being imported (the most poplar brands). These have certified motors (about $10,000 for the testing). Once a motor is certified, than you can import that model year as long as it is under 50,000 mi. In other words, I'm certifying the 2011 Suzuki 660cc motor. Once it has been accepted, I can import them as long as they are under 50k miles.
This requirement threw everyone out of the picture except for about 5 companies. This has also raised the price of a base truck about $1000-$1500/truck (along with dollar/yen & transportation)
That's the latest requirements.
Again, I know of no one that has certified the Subaru or Honda.
A good source for searching the requirements is
Japanese Mini Truck Forum - Powered by vBulletin search EPA and there is a lot of discussion.
pic. is a 2010 Suzuki (same as a '99-'09)