There have been many good reasons why air-to-air combat remains the near-exclusive domain of nation-states. Even the earliest and/or simplest aircraft require trained pilots and ground crews that are not exactly in the greatest supply, and to use them requires a complex supply chain.
Because of this difficulty, the one proven route to the deployment of aircraft on both sides in civil wars is to have a faction’s foreign patron supply and equip them. The few historical examples show this pattern at work, with CIA operators like Allen Pope crewing small numbers of planes to assist allied rebel forces in Guatemala, Indonesia, and Cuba.
Even these met with only limited success-Pope’s A-26 was shot down, and the failure of the “exile” air force at the Bay of Pigs is well-known as well. These planes were effective in Guatemala, which had no opposition, but as they found out over Cuba in 1961, they were no match for a proper air force.
Since then, the increasing complexity has made aerial deployment even less effective. Basing needs have only increased (providing the opposition with a large, vulnerable target), and the types of aircraft that are both worth the effort to deploy and which can provide even a ‘Seconds turn their back to the duelists and then swear under oath that they saw nothing’ level of plausible deniability are vanishingly rare. Given these limitations, any outside opponent wishing to semi-secretly intervene on behalf of native non-state allies would, as multiple nations already have, choose to just use their own air power and merely remain quiet about it. Although increasingly hard to actually keep secret, this fits the narrow “duelist” level of deniability.
With the foreign intervention in civil wars aspect of air power covered, the question then turns to whether there has been an instance of genuinely native air power on both sides in a civil war. The answer is that there has indeed been such a case.
On November 27, 1992, Venezuela suffered the second of two coup attempts in that year. The bulk of forces actually attempting to carry it out belonged to the air force, which gave them a ready supply of planes. However, the entire air force did not go along. Two F-16s with loyal pilots shot down several rebel planes over the course of the battle. By the afternoon, the coup had failed.
The biggest contributor to this anomalous demonstration of air power was the extremely short length of the conflict. The other factors-A fairly large, dispersed air force, and a military divided enough to launch the coup yet coherent enough for both sides to quickly ready their fighters- paled in comparison to the simple one of time. There were enough ready supplies that for the few hours of fighting, the crushing logistical problems could be put off.
To transpose a similar situation into Command while maintaining some degree of realism is quite possible. While unusual, all it takes is some explaining in the briefing/background page, and the placement of each faction’s planes at the appropriate airbases.