If you want a "kit" new parts delivered to you home,then just go to any mustang parts vendor.There are several companies making brake conversion kits.You just have to shop around for the best price.You can start with paddockparts.com, CJponyparts.com, larrysmustang.com,
cobranda.com, johnsmustang.com, calmstg.com, virginiaclassicmustang.com, texasmustang.com,
mustangsunlimited.com, mustangsplus.com, nationalpartsdepot.com, and there are many others.Now if you want to do it yourself and do it cheaper.You can use the front disc brakes and calipers from a Granada or Monarch,you'll also need the outer tie rod ends from the Granada,(get new ones).The power booster you will have to buy from a mustang parts dealer,they have reproductions.It will be nearly impossible to find one on a parts car.And even if you did find one it will cost at least $200 or more to have it rebuilt,so it's just not worth it.You will also need to get brake lines and proportioning valve from the mustang parts dealer too.If it was me I would just get everything new and save myself alot of time and work finding,cleaning and rebuilding all the used Granada parts.It's definately a good swap and I urge you to do it.It's not hard to do with basic tools and the difference in stopping power is like night and day.I've done several of these swaps myself.And remember,once you swap over to disc brakes your wheels, if they are the originals wont fit anymore and you'll have to get new ones.Good Luck!!!