A typical B&W developer might contain:
Metol (a.k.a. 4-(methylamino) phenol sulfate)
Sodium sulfite
Hydroquinone
Sodium carbonate
Potassium bromide
(the above is called D-72.)
You could possibly try acid-base extraction, the developers (metol and hydroquinone) ought to be less soluble in water, and more soluble in organics, when protonated in acid, and the reverse when deprotonated in base. Both metol and hydroquinone would probably come together.
However, you can probably find hydroquinone, from photo chem suppliers, who will sell to individuals. Try
http://www.artcraftchemicals.com/ - Artcraft Chemicals, or
http://www.photoformulary.com/DesktopDefault.aspx - Photographers' Formulary.