There are a number of recipes for selenium toner out there, both the direct and the bleach-redevelop variety. They all call for elemental selenium, which is difficult, poisonous, and hard to obtain.

Dassonville T-7 selenium toner (Flemish Toner)
Solution A - Bleach
Potassium ferricyanide 30 g
Potassium bromide 30 g
WTM 1 l
Solution B - Redeveloper
Sodium sulfide 40 g
Selenium (powder) 1 g
WTM 1 l
Dissolve the sodium sulfide completely, then add the selenium and heat until dissolved.
Use the bleach full strength. Bleach the print completely.
Dilute the redeveloper 1:10 for use. Redevelop until the desired tone is reached. Wash for one hour after toning.

Kodak T-55 Selenium Toner
Hot water 750 ml
Sodium sulfite (anh) 150 g
Selenium powder 6 g
Ammonium chloride 190 g
WTM 1 l
Dissolve the sulfite in the hot water, then add the selenium. Boil the solution for about 30 minutes, then filter off any undissolved residue. Cool, add ammonium chloride, and dilute to 1 liter.
Dilute 1:5 for use. Tone 10 to 15 minutes at 20C depending on tone desired. Tone becomes a bit colder on drying.