There have been some changes in "standing" because of recent firearms cases, I believe in IL and NJ.
Look at that SAF suit in Chicago that is going on now. None of the plaintiffs have actually been charged, but they have proved "standing" (the law potentially damages them)
It would be my understanding that you would need to be a citizen of that county, and a user of that park, in which case you could claim standing because of "potential" injury (this being arrested). Now this stuff is brand new (last year or less) so an attorney would have to read the rulings carefully to see if you would qualify. This is one way to present a suit without exposing yourself to potential criminal charges.
I think the best thing to do is: #1: Physically, and Personally contact the commissioners at one of their regularly schualed meetings...They usually have an "open comment" period. Be ready, be clear and concise, you will probably get 3 to 5 minutes to present your case. Then it will go to "consultation" (county prosecuter), then it may make the agenda for formal comment and finally something done. You may be able to talk to the commissioner that represents your area before hand too.
Of course: the optional method is, take you firearm into the park and see if they try enforce their rule. If they do, you automatically have standing, but then it will not be on your time schedual.