When I tried an early beta (of 10.04) I was unable to find the mosquitto client tools in the software store. Neither does it show up in either list you linked.

When I tried an early beta (of 10.04) I was unable to find the mosquitto client tools in the software store. Neither does it show up in either list you linked. I guess it was left out for other reasons. At one point there was a setting in the software store to show all available packages. It has been removed. At present I am only aware of command line tools for finding S/W that includes all available packages. (`snap` and `apt`) I guess Ubuntu are dumbing down Linux. They have succeeded. I think it's dumb.