I still do have the mSIGNA wallet. It doesn't offer any option to export single private keys. The only private key export option is said BIP32 extended private key.
The problem with the software is, I wasn't able to get it to connect to a node so far.
The .pdf I linked to above says it should connect to your own node. Are you running a node?
Can you import your seed phrase back in to mSIGNA and regenerate the same wallet with the same addresses? If so, then it is hopefully just a case of finding the right derivation path. But I worry given what is written on that .pdf it is going to be significantly more complicated since it uses an unknown multi-sig arrangement.