If you must work with a flat datastructure such as a plain old array, then just use a binary search that limits itself to searching element 0, 3, 6, 9, 12, 15, .. n. You can google for binary search algorithms, and then just modify one to focus only on the first of each three elements. If the number of records never will grow large, a binary search may just be too cumbersome. If that's the case (that the array always stays pretty small), just search in such a way that each iteration skips two elements, so that you're framed to look at records.

On the other hand, I'd say that you're just using the wrong datastructure. You probably should look into using a hash of hashes. You can read up on that sort of thing in the following documents: perlreftut, perldsc, and perllol. For more advanced reading, there's perlref.

I hope this gives you enough to get started.