No one knows for sure if, or how long the Chinese made "Happy Time" engines will still be imported. There are several problems with these engines, the big one is as of yet I haven't heard of the makers/importers trying to get them approved. The EPA only tests engines that are submitted for approval. I think a well set up and broken in HT could pass the tests for off road use, but they must be submitted. Time will tell.
In the meantime there are several Japanese made 2 strokes that are already EPA tested and approved. They are more expensive because they are quality built. The Tanaka, Mitsubishi and, Zenoah(sp?) are some 2 strokes that have been approved. The Subaru Robin 2 stroke may also be approved, but I'm not sure about it. There are also others, I'm sure.
The alternatives are the 4 stroke engines that have been EPA approved.