Is there any insurance agency for a gun owner ?

Firearm's insurance ONLY cover accidents and theft, willful acts of criminal negligence AREN'T covered by insurance nor do insurance companies want to provide it.

"Wherever these proposals surface, insurers have been telling lawmakers that such approaches would not only violate basic insurance principles but also be unworkable.

“Though well intentioned, such proposals misunderstand a fundamental principle of insurance—that it is designed to cover fortuitous, or accidental events; not intentional conduct. Property/casualty insurance does not and cannot cover intentional behavior such as criminal acts,” said Willem O. Rijksen, vice president of public affairs for the American Insurance Association.

According to Jimi Grande, senior vice president of federal and political affairs for the National Association of Mutual Insurance Companies, gun liability insurance measures would neither deter violence nor help victims.

“Liability coverage is designed to protect against accidental damages, most of which involving guns would be covered under a homeowner’s insurance policy. While some policies may provide coverage for liability stemming from the intentional use of a firearm for defensive purposes, no liability insurance product covers intentional acts of malicious violence, whether committed with a gun, a car, or any other instrument that is used as a weapon to deliberately harm people,” said Grande. “It is inconceivable that any insurer would offer such coverage, either as part of a homeowners or renters policy or on a stand-alone basis.”

Grande also said any effort to add an insurance requirement to gun ownership “will be met with strong challenges as a violation of the Second Amendment.”"

http://www.insurancejournal.com/news/national/2013/04/10/287849.htm

There are several policies available...

http://www.gunsandammo.com/network-topics/personal-defense-network/choose-concealed-carry-insurance/

https://mynrainsurance.com/insurance-products/self-defense

it's a standard rider on a homeowner's or renter's policy

I mean just in case you need it for a situacion where you need a lawyer who represent you if you feel forced to shoot

Tons. Gun collectors, as in people who own very old antique guns, insure every firearm they got.

Regressive Insurance Company. Its spokesman is a character named "D'oh."