Look around at granite suppliers in your area.

KEEPING LOCAL BUILDING MATERIAL SUPPLIERS busy while you support them by using there products in your flips.6.  

I'd prefer a wholesaler, small company, or reputable online supplier...

I'm currently shopping around to find a quality Kitchen/Bathroom Cabinet supplier for my galley style kitchen in my condo in the Bay Area.

Any recommendations on supplier to use?  

Because of how turn key companies buy (usually further upstream and not off the MLS) and the fact that they have large discounts with suppliers and better control over their construction costs than the average individual, they don't need to be putting big mark ups on the properties and pricing above market value.

A comprehensive spreadsheet of the specific materials you would use in your rehab is the way to go.Home Depot has a canadian version.http://www.homedepot.ca/for specialty items amazon has alot.http://www.amazon.caYou can also speak with private suppliers in your area.

I guess this is because certain other suppliers have taken a big chunk of the market away?

@Cody Barrett, another possibility for this is if the shingles are not all from the same "batch" some roofing companies and suppliers will offer a discount if they have small amounts of shingles left form different batches, it is technically the same color but when they are made at different times sometimes the color could be slightly different. 

They make special product for this but you need to go to supplier and not abig box store.