There are no chemicals or repellents on the market that will be effective in keeping pigs away. Given their omnivorous nature, it is highly unlikely that such a product could ever be discovered.
Your only control options are
1. Shooting
2. Trapping (given the risk of harm to endangered species, I would suggest corral traps or non-lethal cable restraints.
3. Fencing the field to keep the pigs out.
Additional details on these methods can be found at ICWDM