How to derive a 4096 bit or 8192 bit RSA private key from a (BIP39) mnemonic seed? How to derive a 4096 bit or 8192 bit RSA private key from a (BIP39) mnemonic seed?

Any tool available for this?
As it was already pointed out in a comment by @corpsfini, you could use a PRNG to generate pseude-random numbers from the seed. Then you would check whether they are primes using some probabilistic primality test. 

In spirit the same procedure is implemented in this github repo you might find useful.