I don't know about SLC, but GlassMasters in Layton is beyond awesome. They stayed late for us, got us the baffles the same day, custom fit them actually inside the tank to make sure they fit (turns out the tank wasn't completely squared-off), and then they sanded the edges so we wouldn't cut ourselves.
Some Ace Hardware stores do it, but not all. Call ahead. You usually have to just give dimensions...and hope they fit.