We use mattress protectors which basically enclose the entire mattress and close with a zip - they're brilliant! They don't have a specific brand (and we're based in Aus anyway so I'm sure it'd be different no matter what) but if you can get this sort I highly recommend them - they're like a very fine gauze with a zip and are pretty hard-wearing.
A few other tips (you probably know these already but hey)...
- don't let guests use their own bedding/sleeping bags - this helps slightly to prevent spread.
- metal bunk beds - a lot less places for bedbugs to hide in these (at least in the bed)
Finding out where your guests have come from can help as well - for example if they are coming from a hostel which is notorious for bedbugs you can ask them if they have bites etc.
If you do get bedbugs and need to get rid of them, a steam cleaner is a brilliant investment when combined with insecticides. Steam is one of the absolute best ways of killing bedbugs and their eggs.