I believe the only listed for the purpose boxes can be found in the following links (warning, PDF's):
http://www.woodhead.com/data/current1488/multiple%20outlet%20boxes%20902.pdf http://www.woodhead.com/data/current3054/multitap%20902.pdf

I have seen FS boxes w/ kellem grips used as well, but I am not sure if they are listed for this.