You might find more information in the primary and preschools section. There have been a good few threads on how to get experience there.
The INTO and Teaching Council have clamped down on unqualified people taking substitute work in school. Principals have been given a directive not to hire unqualified applicants. There might be some subbing out there though as I've heard that not everyone is following the directive. However, I'd imagine that any unqualified people are getting the job based on who they know. It's not a situation that I'm very happy about, as I think that there are enough unemployed primary teachers at the moment to cover these days. As I've said on another thread, our Principal splits the class if there's nobody qualified available, but she might hire a secondary teacher if one was available.
Here's a link to a good thread in the primary section
Best of luck getting experience. Maybe if you have Garda vetting you could volunteer in a school that has an autism unit as they run summer camps during July. Your reference would probably be from a Principal/teacher and it'd be in a school setting. We don't have an autism unit in our school, so I'm not sure if they do take on volunteers like that, but it'd be worth trying.