If you are going to sue the federal government, you'll have to bring suit at the Court of Federal Claims. You should at least speak with someone experienced with handling such cases. I worked at the Court and note that there are some procedural steps that must be followed. I would likely recommend starting with a letter to the agency. Either way, discuss this with someone specialized in IP law and with experience before the Court of Federal Claims.
This is not to be construed as legal advice, and I am not your attorney, A conflict check and engagement letter would necessarily be required before any retention or attorney/client privilege exists.
State or Federal?
If Federal, you don't sue for infringement of a trademark, you sue for unauthorized use or taking. I practice at the US Court of Federal Claims and can tell you that you would need a lawyer admitted to that rather unique forum, as pro se litigants are notoriously unsuccessful there. The Dept. of Justice defends the cases as has an essentially bottomless litigation budget, so beware. You want to pursue administrative claims first and also try to get help from your Senator and Representative before going to the USCFC and you don't even go unless it is a big dollar case. Sounds like you are too late for an injunction as to the current event.
If it's a state Gov. contact your State Senator or State Representative or the Attorney General and see if you can get some help. Then, if no help, see an attorney with experience in state claims.
You will want to be sure you actually have a valid name, slogan and logo. The Government tends to pick pretty generic names so I am skeptical as you the validity of your claim.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.