I am very new to the world of bourbon. My only post on this forum so far has been for a search on a 20 year AH Hirsch. So far no luck!!

During my search I realized how difficult it is to find bottles of the 20 year AH Hirsch. I have called more places that I care to mention. It did made me think though. Are there other "Holy Grail" type bourbons out there that are very difficult to find? So far, I am sure of the 20 year and the 19 year AH Hirsch of being in this Holy Grial category. Are there others out there as well?