Has an all-in-one, complete works of Sergei Rachmaninoff, ever been released on cd?

No is the answer. There are various sets of compete collections of different parts of Rachmaninov's output such as:

Complete piano music
Complete Piano concertos
Complete Symphonies
Complete orchestral works
Complete piano transcriptions
Complete works for chorus and orchestra
Complete recordings by Rachmaninov (both of his own and other composers' works)

... but not a collection of ALL his work across all genres.

I suggest you type 'Rachmaninov complete' into the search bar in Amazon (under 'Classical music') and browse through what you think you need.

Good luck!