What Reserve command billets are there for Command Master Chiefs, SELs, etc.?

Yes, I believe there are Command Master Chiefs in the Navy Reserve, serving as senior enlisted leaders and advisors within their commands.

Navy Reserve units have a Senior Enlisted Advisor (SEA). They are typically the most senior ENL. However, most have a primary job outside advising the Skipper. My SEA in one of my Pacific commands was a DKCS who made magic happen on the financial side. She had coffee with me to sort out the SEA stuff going on. The other NCOs knew when she talked in her SEA role, they listen up. Good SEAs are very appreciative of their Skippers supporting the NCO community. After all, we had to keep the junior commissioned kids in line too. Bottom line, there may not be a full time billet for smaller Commands, but there will be a SEA on the ORG chart because you need them.

Command billets for senior enlisted? I don't know about the other services, but in the Army, the joke is that a Command Sergeant Major ain't in command of shit, except if he has a driver. Then he's in command of his driver.