Based on the date in that commit, the image is available in snapshots: https://downloads.openwrt.org/snapshots/targets/bcm53xx/generic/
Unless you're fine with WebUI-less barebones installation, I'd recommend you use the Image Builder from the link above and create images containing all the packages you may ever need in the future, as snapshots change and you may not be able to install certain packages without updating firmware in the future.
@tmomas @bobafetthotmail @richb-hanover the MR26 page needs to be updated: https://openwrt.org/toh/meraki/mr26