I have seen this many times. One time, as a consultant, I proposed a conveyor system to a potential client. My proposal included a suggested layout and price. Two weeks later a local conveyor supply house came to me asking me to help them come up with a design for a conveyor system. The layout drawing they showed me was MY DRAWING with the title block blanked out! My "client" was passing out my drawing to me competition asking for pricing. We didn't do business.
In my opinion, regretfully what you are involved with is straight out theft. Ever heard of intellectual property? Most managers never think of it until its pointed out to them, but the practice of passing the results of one person's work product around to others for competitive pricing is both very common and very unethical, especially if that work is labeled "confidential" or "proprietary". Unfortunately most managers don't really care unless they see the probability of financial loss through a lawsuit. Again in my opinion, if the only thing keeping you from doing something wrong is the threat of a lawsuit, I don't really want to do business with you anyway.
If you ask a vendor for help and he provides a response in good faith, including a technical description of his approach to solving your problem, you are breaking that good faith if you don't treat other vendors equally.
Ask your bosses if they would feel the same way knowing your work is being used by your competitors to undercut your pricing?
I know there is no good solution here because you are a "peon" in this scenario and none of the decision makers (your customers and your bosses) really give a sh__ about that intellectual property stuff. They just want to git-r-dun. They would probably use pirated software too.
I would suggest that you start bringing the topic up occasionally, not refusing to do your assigned tasks, but still letting them know what they are doing. I would also ask them how they will react when they see their drawings being used by their competition because, trust me, that WILL happen. Maybe someday they will wake up and refuse to participate in theft.