I am a sysadmin really, although that isn't my job title.
I deal mainly with HPUX, but some Linux, Solaris, AIX from time to time. I would say that there are a reasonable number of opportunities although the company I work for aren't that good at times for allowing you to follow them but ymmv.
I started by answering an ad in the local paper when I was looking for work after leaving university. I had not done a IT degree, (Astrophysics), and started as a trainee and worked up to a senior team member.