Dry aged beef is not really difficult to find in high quality butcher stores and top-line steakhouses. But it is almost IMPOSSIBLE to find at Supermarket Meat Departments - even the most expensive Supermarket! Because almost ALL large Supermarkets purchase their meat form one of the large national meat producers.
Most national meat producers (and well-known mail-order houses) vacuum pack meat in plastic, then refrigerate it for several days or even weeks. This Cryovac-wrapping is called "wet aging" which produces a tender, soft steak, with little shrinkage - but the flavor is mild - not to say bland.
A dry aged steak is firm, yet tender at the same time, with a nutty, robust, richly beefy flavor - but is very expensive because the dry aging process causes a dramatic loss of weight (as much as 15-20%) due to shrinkage and trimming.
A nationally known butcher named Merle Ellis discovered a technique for dry aging beef at home. Here are the complete directions he offered some years ago for this technique.
Be sure to follow each step carefully, for safety's sake.
1. Only the top grades of beef can be dry aged successfully. Use USDA Prime or USDA Choice - Yield Grade 1 or 2 (the highest quality of Choice) only. These have a thick layer of fat on the outside to protect the meat from spoiling during the aging process.
2. Buy a whole rib-eye or loin strip. [You cannot age individual steaks.] Unwrap it, rinse it well with cold water, and allow it to drain; then pat it very dry with paper towels.
3. Wrap the meat in immaculately clean, large, plain white cotton dish towels and place it on the bottom shelf of the refrigerator - which is the coldest spot.
4. Change the towels each day, replacing the moisture-soiled towels with fresh. Continue to change towels as needed for 10 days, to 2 weeks. (See Step #7 for cleaning towels.)
5. After the desired aging time, you're ready to cut off steaks from each end, trim as desired, and allow the rest to continue to age in the refrigerator.
6. If, after 21 days, you have not eaten all the meat, cut the remaining piece into steaks, wrap each steak in freezer-proof, heavy-duty plastic wrap, and freeze. The steaks will keep for several months in the freezer.
7. To clean the towels for re-use, soak the soiled towels, immediately upon removing them from the meat, in cold water overnight. Next, soak them in cold, salted water for 2-3 hours to remove any blood stains. Then launder as usual. [In olden days, butchers used to cover sides of beef with cotton "shrouds" during the aging process - this is essentially the same thing.]