I want to be able to read photographs from my XQD cards via my new MacBook Pro which has only USB-C ports.
Does any card reader exist to allow me to access my photographs?
To my knowledge no such device exists. You're stuck using a USB-3.1 to USB-C adapter until someone decides to link two niche devices to each other.
The successor to XQD, CFexpress (also known as CFX) is backward-compatible with XQD. The first iterations will use the XQD form factor and connector. However, CFX is designed to use PCIe 3 / NMVe host interface. As such, CFX readers will probably rely on Thunderbolt 3 (or comparably fast interfaces in the future).
Your MacBook Pro's ports are dual-mode USB 3.1 and Thunderbolt 3, over a USB-C connector. So for high-capacity high-speed media connections, you should probably be looking at Thunderbolt 3 interfaces.
One such CFX reader that relies on Thunderbolt 3 is the Atechflash Blackjet TX-1CXQ. (Rather, it will use Thunderbolt 3, when it is available on the market. The manufacturer previously had announced the VX-1CXQ as available 3rd quarter 2018, but the product page is no longer available.)
Blackjet's UX-1 Cinema Dock supports XQD 2.0, and also connects via a Thunderbolt 3 USB-C connection. However, at $425, it seems a bit pricey.
Prograde Digital has demonstrated a 1 TB CXExpress card with a prototype CFExpress/XQD reader that also connects via Thunderbolt 3. However, their anticipated September 2018 release date for both card and reader has passed.