If you live in Southern California, you ought to be looking for JM varieties that can take a lot of heat/ dry weather and limited cold in winter.

There are hundreds of Japanese maple varieties that fit the "lush green" description. Are you looking for an upright tree, a weeping threadleaf variety, a dwarf? I would suggest visiting a few web sites that offer a range of maple varieties and compare their photos and descriptions. Some good starting points are: www.mountainmaples.com and www.worldplants.com. Both of these are west coast companies. Mountain Maples, in particular, has a good search function and pages categorizing maples by type.

Back to your original question, one of the lushest green JMs I have seen is the relatively common Viridis, which is a green dissectum (threadleaf) weeping variety. It is an old standard that has been around for years, and easy to find in nurseries or even big box stores like Home Depot. If you want more of an upright tree, Seiryu has similar leaf color and texture, but does not weep and gets much taller.