My answer: "99.9999% of school districts arenít going to approve an invitational for 10-20% of their school population during a school day. UIL maybe. Random contest? Much less likely."
My answer, rephrased: "It's very unlikely that this contest you're hoping for actually exists. It's prohibitively disruptive to the educational environment for nearly all high schools to allow what you're asking for - an invitational optional marching contest during the school day - so you're not likely to find one."
Your answer, rephrased "A school district used to, but they're not in your area, and they may not do it anymore. So literally nothing I'm saying is actually answering your question, and I'm just criticizing the previous poster for telling you that you're not going to be very likely to find a contest."
Which of those is a more complete, useful answer to the OP's question?
(And as to my math: there are 13,452 school districts in the USA. Finding ONE [Mineola] that offers a contest, albeit 3 hours away according to Google Maps, is within a reasonable margin of error for 99.9999%. Considering the other 13,451 districts do *not* offer said contest, or are not in the North Texas area.)
To the OP: Also, consider talking to some of the larger districts nearby or within a reasonable driving distance. Perhaps one or two of them offers an in-district Pre-UIL evaluation, and you could get a slot in that for a small fee?