I found mine on e-bay some years back.
Make sure you have the model #, and correct options that you want for that Ruger ?
Also, sellers descriptions can be misleading, intentionally, or not.
You are looking for a fairly old holster which may or may not have been treated properly.
Soaked in some sort of oil is one of the most common and worst mistreatments which can occur.
Lawrence used the 100 as the model. Earlier holsters had more numbers and letters, depending on options.
As listed in a 1969 edition of Shooters Bible, 601 was the size for a Ruger Super Blackhawk with a 7 1/2" barrel.
BTW, neither the holster or the Bisley is for sale.
The letters on the holster after 100 means Glove kip lining, sight protector, brown lacing, sewn in end plug.