It's so exciting to hear that you're planning to pop by in May.
What I would suggest when planning for a last-second visit is reaching out to the tour groups you're interested in joining, to see what their policy and openings might be. They'd be best able to advise on this subject.
There are a number of tour groups
available, especially in Dublin
. They might have some options available to help with this issue.
There's also a wonderful accommodations finder
you can you, which can make it simple to find a home away from home. I've set it to find spots in Dublin, but you can easily change the location, accommodation type, and star rating to narrow down exactly the kind of accommodations you'd like.
I hope that this helps! Please let me know if you need any more help, or would just like to chat about your upcoming adventure.