I doubt that any of the existing oem or aftermarket inserts will fit because they are made for different models. Besides the 6159 Tuna has a one piece bezel. AFAIK the insert is made of acrylic with the numbers engraved from beneath. Once the insert is gone it's most likely that you have to replace the whole bezel, which unfortunately can be a long shot regarding your 6159 Tuna.
I wonder if a custom (non-acrylic) insert could be made for an original bezel that lost the acrylic insert....:icon_scratch:
The bezel I purchased has a nice channel for the insert. I am guessing that getting the original will be impossible to get my hands on but I would be happy with an aftermarket at this point. I'll keep looking for them in the future and hopefully I can buy one.
I will post details of whatever I end up with as an insert but know that I will have something installed in the bezel