Thinly sliced available at Japanese supermarkets is not sold overseas. If you order from the butcher directly it you can get it, but since there is no custom of eating thinly sliced meat overseas, it can be tricky.

When trimming the meat block in step 1, don't divide into smaller chunks. Freeze the meat in a single block as it'll be easier to slice.
You need to put your weight when slicing the half-frozen meat, so it's pretty strenuous. If you don't have a lot of strength, try defrosting the meat for 3 hours! Or, use a serrated blade knife. Recipe by Popotankobu