Do they even MAKE cassettes for road bikes with gearing that low?
Yep. They're generally meant for touring bikes. I think Snapdragen has a Shimano Deore rear derailleur on her road bike, with either a 32 or 34 tooth rear cog. Wish I had one of those sometimes !

Don't forget to ask your LBS what's the largest cog your current derailleur can take before you start talking about swapping derailleurs.

So what's the gearing on your bike currently?