There are quite a few but most are for mounting external 3.5" drives like a floppys, etc. For hard drives, you might want to look at mobile racks for just one drive. Look under Hard Disk Accessories on Newegg for something fancier than just a pair of brackets and some screws, which is what most HDD adapters are. There are both mobile racks which allow drives to be interchanged and drive coolers for just holding one drive. And for multiple drives there are drive racks from Lian Li, Silverstone, Cooler Master, etc. that hold up to 4 drives in up to three 5" bays.
Not having tried very many types of mobile racks, I can't offer a lot of advice except to say that most are pretty long, so clearance at the rear may be an issue with your case and or what you have in there already.
.bh.