I found this article somewhere on the internet. Regretably I don't remember the source of the article. But here is the original German reference.

"Found this online, as quoted from "Agfa Rezeptsammlung," "Photochemikalien und ihre Anwendungen," by Dr. Eduard Schloemann, from around 1952. It provides an alternative, using commonly available chemicals, for those who don't want to use or don't have dichromate or selenium. It can also provide a greater degree of intensification than selenium."

Solution A
Volume to Make 32 oz
Citric Acid 3 g
Hydroquinone 3 g

Solution B
Volume to Make 32 oz
Silver Nitrate 5 g
Combine 100 ml of A with 10 ml of B. Bathe your negatives, then use stop bath and fixer.
10 minutes in this gave a two-grade boost in contrast as printed on Ilford MGIV

Note that silver nitrate is corrosive to skin and stains everything it touches.
There's no real reason to keep make the stock solutions separately. In fact, solution A probably doesn't keep. You can mix it up on the spot like this:

Volume to Make 16 oz
Citric Acid 1.5 g
Hydroquinone 1.5 g
Silver Nitrate 2.5 g

I used it with good results on Delta 400 120. There was some staining outside the image area. An accidental half-hour bath produced even more contrast, and this time also staining in the image area, but that could have been caused by lack of agitation.