So as not to hijack Jim's classified ad, I thought this might be of interest.
A young, Eric Kettenberg also marketed such a product many years ago. At the time, he was just finishing construction of his gun shop and his two kids were about knee high to a grasshopper. He gave me several bottles of his concoction to try.
The label reads:
Nitrate of Iron Staining Medium
Historically accurate as applied to wood,
horn, leather, fabric, etc.
While frequently discussed here as a gunstock stain, none have ever talked about its other uses. I did stain a shooting bag with it with good results.
I don't suppose anyone else ever used it.