Hi, With the Internet and international shipping, getting samples of a tile you see on Houzz sent to you is a viable option. Then having it matched would be easier. Though. Come to think of it, is international shipping and ordering on line cheaper than custom manufacture? Look into both!

Not my approach, as a company, to trust chemical/mechanical bonding of glass shelving in a bathroom environment. More than likely the shelves are supported by the tile. I do not attest that epoxies and silicone would not hold the shelves, just not what I would specify. No risk reward for doing so.

A good tile installer that knows what he is doing, can easily remove that single piece of tile.... carefully replace it with another one. Do you have another extra pieces of the same tile? Do you know what brand and color the existing grout is? That will be more of the issue trying to get the grout match to match up or the finding the same tile (in the same dye lot) if you need to buy another tile. Did the heat cause the break or did a pan bang into the glass? Consider installing a heat resistant Lumicor or 3 Form panel behind the stove. Any flat material that can be sandwiched between two resin panels. 1). Crushed glass. 2). Fabric. 3). Fabric. 4). Fabric.

It looks like etched black glass.