Brewer; try Richelieu. Do you have any contractor buddies who can buy there wholesale? https://www.richelieu.com/ca/en/category/?stateProv=ON
Home Depot in Canada carries their stuff as well.
As for the expense, look at it this way, you're only going to do this once and hopefully it'll last you for decades.
Bite the bullet and do it right the first time. Full extension is absolutely the way to go. Sure as Hell the item you want will be at the back!
I finally got all my fasteners organized by type (RH machine screws in one drawer, FH wood screws in a another,etc. )and I just wish I'd done it years ago.
With one hand I can open the drawer, reach in and grab what I need, and close the drawer. Don't even need to put the brewski down...