7404 and 5691 tube available or substitute?

Hi all.
I have a set of cary slm 70m monoblocks. I don't need them yet, but I was browsing out of curiosity. These amps use a 7404 and a 5691 tube. It seems there are none on the market. Is there a substitute available for these or am I in for trouble when these tubes quit.
Thanks for any help
For the 7404 I found this on Google

For the 5691
Looks like several to choose from
Thanks for the help. I feel pretty dumb on this one. apparently the 7404 is the production date in this tube. It is an RCA and looks like its from the 70's. I have been told that this tube is actually an OC3 voltage regulator tube. Does that sound correct?
I'm not familiar with Cary. Nor am I a tube expert. In fact I got my Octave about a year ago and am trying to learn more about the tubes I can use. Just google it. I responded to your question because I would hate for someone to think they have to retire a tube amp because of availability of a tube.