Well, here's a couple of ideas that will brown your parts but remember, there are some good reasons that they are seldom used by anyone who wants a nice even smooth browned finish.
Being in a rural area I'm sure you know the rust finish that most like is the hard brown rust that forms on your shovels and hoes, not the soft red rust that's on your hinges. :grin:
Salt water mixed with a bit of soap.
The metal parts will have to be absolutely clean and free of all oils including the oily fingerprints you will leave when you handle the part.
A solution of 8-12 percent salt in water will form a layer of rust given some time to work at room temperature if enough humidity is in the air. This may require 10-15 applications giving each time to work. Rub off the loose red rust that will form. It will produce a gray/brown finish.
Boiling Salt water using the same mix will produce a better, darker browning in 3-4 applications with the soft red rust removed between applications.
Salammoniac dissolved in water at a 0.5 percent solution and used cold will produce a brown/black surface with 5-6 applications.
A boiling 2% salammoniac solution will produce a dark brown/black with just a few treatments.
Six parts zinc chloride mixed with 4 parts Olive oil applied to a very warm barrel will produce a green coat that will change to red and then to brown after it is neutralized with a 5% solution of caustic soda lye water.
These came from the book "FIREARM BLUEING and BROWNING" by R.H.Angier.
Household chlorine bleach diluted to about a 5% bleach to 95% water will cause rapid rusting. It may take several coats to develop the browning.
A stronger solution will increase the speed that this works but if it is too strong it will start to eat holes into the surface.
Neutralizing this stuff isn't easy and if it isn't totally removed it will continue to rust the surface.
My recommendation is that you take the time to drive into town and pick up your factory made browning solution. You'll probably want to check out all of those ads from the mail order houses anyway.