Where to buy MDF spacers?

Brian,

I had 0 experience wood working before making some MDF brackets a month ago.

Go out, buy a $20 black and decker jigsaw and a $10 sheet of 3/4" MDF and have fun with it!  They are actually really easy to make. 

Trace the speaker you'll use (a paper cutout probably came w/ the speaker), mark the hole locations, and start cutting it out.

Tip:  you can always _increase_ the size of the hole with a drill bit but can't decrease the size of the hole, so make your cuts on the inside of your lines.

Brian,

Regardless of your skill at it, I  think you should try it yourself.  Every one of us who have even the smallest experience had to start somewhere.  The tip that Kfr01 gave is absolutely correct.  I would only add a painters respirator mask and not the cheap paper masks as mdf is a real dust maker. I mainly use it myself because I'm asthmatic.  As far as the skill/sabre saw,  here's one that's a good starter for you.  I actually did my first set of adapters out of 1/4 inch plywood (easier to cut and it's cheaper) just to get myself comfortable with the cutting.  They came out well. 

Hope that helps.  It's really not as hard as you think. 

Duane...

If you think you're confused, imagine how you feel.