I believe Vector was the only company that produced good clones. but they went out of business.
Based on the info I've gathered over the years, the MP5 is a bit more complicated and more expensive to make then many other semi auto 9mm carbines. Of course there is collector value for MP5 clones, but otherwise there are similar weapons for a much lower price.
In my opinion, for a CQB weapon, the MP5's operating system is totally uncalled for. I'd guess that most in the market for a 9mm carbine really aren't looking to drop a grand for something that will not do anything much more than a half priced alternative.