The bracket and brake lines are usually what rust through but that valve is made from cast iron or forged iron and lasts forever,just soak the bracket bolts and lines with deep penetrating lube for days prior to removing.I don't know if that part is available aftermarket.
At least one day before replacing the brake lines spray them with a deep penetrating oil:
AeroKroil Oil (from Kanolabs)
PB Blaster
Liquid Wrench
Toyota Rust Penetrant or High Performance Penetrating lube
Rust Check
Sidney
Repair tv's,vcr's,home/car audio out of my home
E-mail:sidneybek(at)yahoo.com
Dartmouth,Nova Scotia
Canada
1985 Toyota 4-Runner,22R-E,W56,RN60LV-MSEK,rusted rear step/towing chrome bumper with 241 000 KM