If you do not know your product you takes what you's get's!
For instance: Once upon a time I needed a relatively rare Mercedes-Benz piston for a M-B that had a production run of only 7000, very few of which made it to the US. The US version had a lower compression rating and I had a European model to boot. The friendly people had the M-B warehouse, there's one on each coast, informed me that while they did not stock such pistons they would be happy to order me one on their regular stocking order, and I would have it in hand in ten months for the nominal sum of $1100 at current exchange rates. Desiring to drive to Michigan from New York on eight cylinders versus seven, and further desiring to make the trip within the next two weeks, this was decidely inconvenient. Not to mention that the cost was approximately ten percent of what I'd paid for the whole car, and for that sum I could have a full set custom cast out of my material of choice!
Upon conferring with a few friends in the foreign car market in NY I was advised that perhaps I'd best contact Mahle, the piston manufacturer. Lo and behold I found that Mahle has a corporate office in Chicago and Dieter turned me over to his secretary Hildy who called me back the next morning, a Thursday, to inform me that I had a very expensive piston. Hildy calculated the exchange rate and came up with $102 and found it a seat on the Concorde for an additional $58. Tuesday morning DHL handed the little baby (well, not so little-it had a 4" diameter!) to me at 9:50am and I departed for Michigan Wednesday night.
The lesson learned was to talk with everybody you can. Eventually you will talk with somebody who knows somebody within the company. (btw, Dieter and Hildy did not ask for, but received, a rather nice single malt Scotch for their troubles) That person's phone number is priceless. Five minutes conversation with him results in five minutes conversation with his friend who knows something about what you need. Those conversations do not happen through the official company switchboard.
To do any of this, you have to know your product and the supplier of the component parts of your product. A casual example of this are the Ridgid power tools you see at Home Depot. Ridgid does not make the majority of those tools, they're branded for Ridgid by somebody else. (I suspect Makita is a supplier) Research the company that makes your product. Find out what companies they've bought out (it might have been somebody else's product first) and find out who their suppliers are. Find out what the suppliers business is, you may not obviously know. If you find out that your engine manufacturer has a supplier that does tubing bending you've probably found the source of your engine's intake and exhaust manifolds. You'll probably find a part number that they will recognize on the manifold. When you call and they ask you what kind of engine it's on, you ask them what engines it went on. And that's how you find out that maybe your neighbor's tractor has the same manifold as your boat motor.
Alternators are an easy thing to do this with also. I'm incorrectly convinced that there are really only six alternator's in the whole world, three of which are made by Mitsubishi. Every time I need an alternator I go to this little shop out in the country, they operate out of a glorified shed, and they always have my alternator on the shelf. And every time I find that my alternator goes in a bunch of things I never imagined, like a backhoe or something. Very few companies make an entire product themselves any more, and if you know your product and it's component suppliers you can find things at substantial savings. It does take some time but, by talking to the people you meet along the way, you find out about other components that currently might not interest you-but might later.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.