older apps no longer in the store?

I have apps on an older ipad & I bought an upgrade. I want to restore my old one for my son & he wants a few of the apps I have but I can't find them in the app store anymore & they no longer show up in my purchased list, but I know I bought them b/c they are on my new one as part of the back up & setting it up etc. But now since they won't play b/c of ios issues I figured he can add them back to the old one which is now set up for him & when mood strikes I'll play on that one again. Any idea how to get them back? This is annoying b/c I paid for them. I get it if they were free & removed from the app store but things I paid money for, I should still be able to DL right? Am I just missing them in my paid for section?