I totally disagree with your impression of the name Acorn (I think it’s good, but blatantly obvious), but, just as I thought, there’s already a bunch of Acorn Marketing, Acorn Management, etc., type companies out there. Even a few “Acorns” in Australia, including Acorn media and Acorn Capital Limited. I’m not sure why you’re focusing on the “corn” part of the name. I don’t think anywhere hears “acorn” and confused it or focuses or even notices the “corn” in the name. I think Oh, I get it. From an acorn (of an idea) grows the mighty oak (of implementation/marketing).
Warning: brainstorming ahead.
I’m a fan of off-the-wall branding; it can backfire of course but I favor intrinsically attractive words and would stay away from the word “marketing” all together, especially for non-profits.
Of course this is all my two cents, but I have cougha few years*cough of communications work under my belt.
So, think of words you like to say and things that put pleasant, get-things-done thoughts into your head.
So what are your suggestions, Miss Know it All?
Creamery Creative
Purple Prose
Silken Inc.
Cotton Collective
Jack and Jane
Glow
All Aglow (say it out loud. Groovy)
For years I’ve said that if I were going to incorporate and become a vast conglomerate, I would name my business Excellence. Or maybe excELLENce. It’s a visual thing, not as effective in spoken form — but it says “Ellen is Excellent” and that’s the most important thing. 
I have worked with a PR agency called 2 birds talking, which for would be an ideal sort of name. Evocative of the service offered (birds noisily chatting, birds on a telephone wire, sharing information), but it’s also set up by two women - 2 birds. It’s fun, memorable but ultimately serious and no need to have any qualifier with it. I guess that’s what I deep down want to find, and sounds like some of the professional advice is hinting at as well.
i think we need to brainstorm this more, but maybe more in the direction is something like “Count of Three”, based on a quote which suggests we all work better when we work together. You get 3 people who are willing to put their backs into the job and help pull together.
We also quite like The Revery, based on the Emily Dickinson poem (although this wouldn’t be familiar to Australian audiences). But it’s not a 2 Birds Talking, or Two Trick Pony or any other fun name like that right now.
Triple Threat
Three Ring Circus
Three Squares
Beck & Call
The Flexible Sidecar Company
Three Wise Melbourne
Boardroom Eyes
I think I need coffee. Which reminds me that I am having coffee with the ex-MD of a large branding agency next week, so might be able to pick his brands too (ha, autocorrect is funny.)
Ha! 
Why not Girls From Mars Marketing? You’d never forget it, at least, though not sure whether or not you want to give the impression of spaciness.
I think the boy in the group might not appreciate it!
Just a random thought from my inner 12-year-old regarding “Big Red Pen”…I’m fairly normal in the dirty-mind department (not too much, not too little) and it took me about three seconds to add two more letters to the end of that, then snicker.
If I did it, others probably will too. Might not be the image you want to foster.
Working on the “Three” theme: how about Power of Three?
ThreePete
Tripolar 
Treble Clef
Triangulate
Clockwork Marketing
The Kingpin Consultancy Group
This and That Marketers
Tres Marketing
Brand U Day (giving BUD as the acronym; both new growth, and friend)
Advancing Hungry Brainstorm
Unspeakably Cr8iv Things
Pow wow BOOM!
Skid Marketing (only because it made me laugh out loud.)