Could someone kindly point me to a mod that adds crossbows to regular loot/stores in as natural of a way as possible? Would like to acquire one without having to travel to the Dawnguard Fort...

A simple search of "crossbow" from the http://www.nexusmods.com/skyrim/? brought up 67 files ( + 24 that were skipped due to my preferences).

I'm sure you will find something to your liking...