I am very sorry for the delay of the answer. I hope an aswer is still useful for you:
1- Hundreds of classes have been identified so far. Actually, only 5 (number 1 to 5) stand for mobile integrons involved in the dissemination of antibiotic resistance, the others being SI of a wide range of species. Some recent papers reported discoveries of new integron classes through the IntI specific detection
2- What do you mean by class 4 integron ? It is ambigous because the chromosomal VchSI has long been called class 4. The true class 4 is the one most often referred as class 9 (intI9) you could found at the access number AY035340 and discussed in the corresponding paper. I think you should design primers in the attI site, as it is highly specific of an integron class
3- I can send you the paper by mail.