Not even once? Really?

How about that 70s campaign to "Give a hoot, don't pollute!", or any number of environmental groups which have conducted education/advocacy campaigns to encourage individuals to recycle, not litter, etc. Or at a more upscale level, environmentalists who have founded "socially responsible" investment funds, giving individuals a chance to target their money at firms that have good environmental records?

You could also point at the Environmental Defense Fund or other enviro think-tanks/advocacy groups that promote market-based policies, such as tax credits or tradable permit schemes, rather than centralized "command and control" regulation.

How about the Nature Conservancy, which uses privately donated money to purchase land themselves? Or the volunteer groups that clean up trails and riverbanks?

Of course, if your definition of environmental activist is "one who advocates centralized government programs", then of course your statment is true, if trivial (and also typical).