Cabelas, Walmart, Eagle Optics. The Crooked Horn Outfitters model seems to be particularly popular with hunters. The bino system serves basically two functions. One, to elevate neck straing caused by the weight of the binocular and, two, to keep the bino close to your chest as to avoid getting in the way while hunting.

In my opinion the bino system is not necessarily needed with the Monarchs for the first purpose I mentioned though it would prove useful for the second.