TargetTalk

I have a Junior on my team that has to wear a leg brace due to a degenerative condition. I am certain he qualifies as a Para athlete.

What are the rules regarding 3 position and air rifle para shooting.

He can shoot prone like any other kid though. I even think he could shoot standing/kneeling but would require the leg brace to stand which would disqualify him from standard shooting rules if I understand correctly.

I'm going to go out on a limb here and answer this based on your shooter not being para eligible. You have to be hurt pretty bad to get there...... HOWEVER in our normal contests, the rules allow for a medically necessary accommodation/deviation from the rules.
You just need to carry a letter from your doctor mandating usage of the device....... I lost a bunch of my right foot to flesh eating bacteria, but not enough to meet the requirements as a para athlete, thankfully...... My foot is not stable enough to walk without damage if I don't walk on a carbon sole stiffener in my right shoe. That wouldn't normally be legal, but it's an allowed accommodation for me as it is a prescribed apparatus from my doctor so I can walk, and I carry a letter because I'm always squeeky clean on the rules.
If you qualify as a para athlete and that process is real specific, the rules change almost completely as all para athletes compete against each other in their own class with their own rulebook....

Glad to hear you are working with a young athlete with a physical disability.
This is a great sport for many of them and they often have a profound impact on the club/team.
Many of their events are similar to the able-bodied events and relatively easy to include them.
NRA and CMP have different ways to handle various disabilities. USAS governs the Paralympic shooting sports in the US.

You have not provided enough info to determine if the athlete is eligible for international (World Shooting Para Sport) competition and may not be able to here . The process is called "Classification" and the rules and relevant info are posted here:
https://www.paralympic.org/shooting/classification
If the athlete thinks he/she is eligible, click on the Medical Diagnostics Form link and have their doctor complete it. SOMETIMES a Classifier can make a determination of likely eligibility, but final evaluation is always done in person. e.g. a missing limb is qualifying, a braced joint probably requires an examination and tests. I don't think USA Shooting has hired a Para Coach to replace Will Anti yet, but you can PM me if you need more help.
Event and adaptive equipment rules are on that same website as well as https://www.usashooting.org

While I was the Para Coach we developed a very basic shooting table by bolting a piece of plywood on top of a walker. Adjustable, stable enough, portable and cheap (used walkers from Goodwill, etc.). Your shooter can be seated. Rest 2 elbows on the table for "Prone", 1 elbow rested for "Kneeling" , elbow on hip for "Standing". Sound familiar?