There is a logical inconsistency in your argument, is there not? It's one that sits at the heart of every religion: God is invoked as an explanation for the existence of everything, but never needs anything or anyone else to explain God's existence itself. Presumably you'd admit this point, and I'm not mentioning this because I think it's a fatal flaw. My point is, though, that in allowing God to justify its own existence, you are in reality allowing that *something* must be capable of explaining its own existence.
All of this leads to the following question: why does a scientific law necessary need a law-giver? Why are scientific laws incapable of justifying their own existence? What is it about them that you think relegates them to the status of "second causes"?
It may be that you have good answers to these questions, but "a law requires a law-giver" is not such an answer. I'd suggest that this answer could only work in the case where the law in question is essentially arbitrary: where a choice had to be made, between (at least) two equally viable outcomes.* To take a particular example, God's laws in the Old Testament are, at least superficially, arbitrary: Lev. 12:4 states that a woman should wait 40 days (7+33) after giving birth to a son before being considered "purified from her bleeding" (and twice as long for a daughter), but I don't think that there can be any serious attempt to justify that precisely this time limit, and precisely double it for a daughter, was the only theoretically possible such limit. Why not 28 instead of 40? The Bible is obsessed with the number 7, after all, so 4*7 days would fit with this fairly naturally. Why double the time for a daughter? Why any time at all, if it comes to that?
Regardless of the rights or wrongs, though, the point is that a choice existed, and that another choice would clearly have done just as well, and so it stands to reason that somebody must have made this choice. There is no fundamental reason that 40 is the necessary answer to this question (or, if there is, I'd love to hear it).
Compare this with, say, the scientific Law of Conservation of Energy,
which states that the total energy in the Universe remains constant (although it's allowed to change from one type of energy to another). As I was drafting this post, it occurred to me that the Law is actually broken within our Universe, but what's important here is that it is easily possible, within physics, to understand where the law comes from and under what circumstances it would be broken. The law is therefore not arbitrary: it doesn't follow from a choice, or from observations that may have been flawed, or a convenient approximation, but from clear mathematical principles. Specifically, you can prove that conservation of energy is guaranteed in a Universe that is physically the same today as it is tomorrow: that is, a Universe that behaves in the same way no matter what the time is**. As a result, I'd argue, there is no need for a law-giver. This, and other laws, are inevitable consequences. No choice needed to be made: Energy was either conserved or not because of how the Universe *is*.
Still, none of this proves that the Universe doesn't need a law-giver. You might answer that a choice needs to be made about how the Universe is, after all. But it does prove that you have to understand more completely the nature of Universal Laws before making the assertion that "laws need law-givers". They are simply a different kind of law.
(Asterisks * and ** will be added below.)