Guns international has 14 Parker Repros that meet the specifications.
www.gunsinternational.com
Or a person could look for a couple years and find a couple originals and try to get the cost below $20,000. Its the single trigger requirement in a 28 that makes it hard to find.
There is a 24" CHE 28ga, double trigger though, that is available privately. A nice gun. Be a perfect grouse or quail gun. I use a 20ga 24" DHE for that. I can't afford 28ga cartridges.
Or a person could get a brand new AAHE 28 ga with his choice of trigger, barrel length and other features. Might take 6 months to a year.