How to get discount prices for replacement parts
I used to buy my appliance parts at Amre Supply, and never bought anywhere else, so this is only one data point.  But one time I was flirting with the checkout girl and she said "you know, if you make a business account you'll get about a 40% discount on nearly everything".  All it took was an online application and a business card, which I had for my computer software business.  I just checked the "other" box on the "what kind of business" question.

After that, I just identified by business name and got the discount.  

And lest you think it was my James Bond Socializing Skills that got me a business account, I just printed the application online and brought it in, about a month later, where it was handled by a 67 year old retired plumber.

So maybe you just need to pick one place and ask if they have business accounts.  Ya never know.