Can a corporate have their own OpenPGP certificate server instead of using the public ones. If so, where we can found the server software? is it available on Linux?
yes, anyone can run a OpenPGP key-server, which mainly distributes pubkeys.
There are a number of Free Software products available that run on GNU/Linux systems,
for example https://git.sumptuouscapital.com/?p=sks-keyservers-pool.git;a=summary
running https://sks-keyservers.net/. The idea is that all public key-server sync their pubkeys.
However the trust giving capability is not done by such a key-server, in a classic OpenPGP trust model it can be done by an organisational part that signs the pubkeys to be trusted with their key. This would be like a certification.
We do develop a new method for distributing pubkeys more easily right now, called WKD/WKS, see https://wiki.gnupg.org/WKD. As an organisation this is probably the
best way in the future to distribute pubkeys for email addresses of the organisation.
I hope to have addressed your question adaquately.