One freebie place is www.eventspan.com - Since you don't have to pay, there's nothing to lose. You can also pick up some promotional widgets that you can place on websites.

Since you are going for such a specific niche audience, I'd try to find blogs or forums in your space and see if the author would be willing to mention your event.

Finally, with a specific topic like that, search ad sponsorships might work for you.

Good luck!