Check in your home area for some local archery clubs. See if any of them have a Field Range (3-D shooting ... or shooting at one target per site, then moving on to the next, and so on). If you ask real nice, and explain why, after they stop laughing (Yes, been there, got that! ) they might allow you to "borrow" their range for a 3-D blowgun shoot (especially if you offer to pay for the use ... translates to you'll need to charge a participation fee).
Bruce Bell tried to get the Wayne, NJ archery club to host a blowgun competition on their turf - they wanted (a decade ago) over $250. Worst part, it was not even being used for the date we were looking to host.
Near where I live, there is, in Upper Mt. Bethel, PA - a county park, free archery area - Bear Swamp. I was able to reserve it for free a decade ago (now a fee is required) for the first International BG Competition. Here's pictures on our sister site (slingshotforum) http://slingshotforum.com/gallery/album/1772-bear-swamp-archery-complex/
Check out the hand drawn map. It takes 30 minutes to stroll the loop, so I set 30 minutes as the maximum time to complete the "biathlon" style blowgun shooting competition (Cherokee style - like they shoot at their annual gathering). If you use 2-D (bulls-eye) targets, score is first, if a tie, time is the tie-breaker. Over 30 minutes - disqualified.
If you make it happen, please post photos, would love to see it.