If you only needed to do a couple, a concrete block wall shold be able to be drilled with a carbide holesaw. Note, if you hit a rib, it would be a big pain whatever you used. The centerhole bit can probably be found with a carbide tip, or, just drill the hole with one, then, the bit is just a guide. In fact, you could just use the shaft and not dull it at all. Once the hole saw is started, you don't need the center bit but you need to be careful. Diamond core bits often do not have a center bit, and it is an aquired skill to start them and get the hole where you want without it walking all over the place (this would probably work with the hole saw as well). Basically, you start with the drill at about a 45-degree angle so only a little edge is cutting, once it makes a decent divot, you slowly pivot the drill so it is perpendicular to the wall and finish the hole.