Max....look to your bean counters... Here's what I use to run up against at my old company. I would do as you do, shop for the best product, at the best price, with the best delivery or availability. That never changed. I was in a position to fight it there. My bean counters would get bills from several vendors, and the first thing they would ask, is why don't we just deal with one, it would be much easier. I explained to them I would pit one against the other on certain parts, to keep them honest for one thing. But, to also save money, and time, if one kept a better supply than the other. Sometimes one vendor would have close outs on certain products we used, and I would take advantage of that when I could.
The company I work for now, goes to one vendor, and they have cheap parts, slow shipping, and low inventory. I just laugh as I bide my time. I will put in for this position when their guy retires in a few years. He is costing them thousands of dollars each year by not shopping around, let alone the down time....you are spot on Max...give'em hell...