Are you certain it's not SRAM that designed your crankset or Shimano? The specs for the Spesh' Turbo Tero X4, I looked at said the crankset is SRAM.

Despite the apparent ease of changing just the small ring, SRAM might not sell the rings individually. And the shop might not be willing to put third party rings on your crank for a various number of good business reasons.

You might be able to find something yourself and do it. Or even find a small shop willing to do it. But if there are warranty issues later, your non approved fix might void them.