What you will have problems to retrieve is the ca.key. The ca.cert is distributed to the clients alongside the client.crt and client.key. You should be able to get it from there.
The ca.key on the other side not distributed and it is what is used to signing server and client certificates.
The whole point of the PKI, Public key infrastructure, is to make it practically impossible to retrieve the ca.key. So trying to regenerate the key is not something that you want to even consider.
You have to generate new certs and distribute them to the server and clients and in the future keep your ca.key and ca.crt safe.
Eventually you have to do this when the ca.crt expires, default is 10 years. That is if you do not need to create more clients before that.