The first question is how serious is this leak? If, for example, you
can see it through a window and it serious enough that it can be doing
damage to equipment, wiring, etc, then I would get the water shut off
outside immeadiately. That is well within any landlord's rights. I
would take a photo of the leak too, if possible, or at least have a
couple witnesses present that can verify that there was a serious leak
and what you did.

If it's not an immediate threat, then I would try revisiting the local
police/sheriff as others have suggested. You may find someone
sympathetic to helping you gain access and it doesn't cost anything to
try. In every state that I'm aware of, a landlord has the right to
enter after giving reasonable notice. And for a true emergency, you
can enter without notice.

If the police won't assist, then the logical next step is getting an
attorney, unless you are knowledgable about how to go about getting a
court order yourself.