Gerpins Farm, only has a couple of microlights based and its pot luck to find anyone there.
At Damyns there are a number of Jabiru, Flight Design CT, Vans RV- and other GA and microlight types based. Not sure how many are group operated.
If you are prepared to consider Earls Colne then Andrewsfield should added to your options to consider. Its only 15 minutes from the M11. I have found it to have a good social feel to it when visiting and there are a variety of groups there.
G-APDK