There is no such thing as an mIRC server. mIRC is simply a client (one of many) that can connect to IRC servers.
There are many companies that will host an IRC server (IRCd) for you, you can search Google
Also, if you want an IRC server just for your friends it is possible to host one on your own computer, provided you have a box that is up 24/7 and a quite fast always-on connection. Preferably the box should run an *nix, but there are IRCds that will run on windows (e.g. UnrealIRCd
You can find a list of common IRCd programs here
, just search google for their names to find their homepages.