RU-486 or Mifeprex is taken to during early pregnancy. 49 days (7 weeks) or less since your last menstrual period began. When you use Mifeprex (Day 1), you also need to take another medicine misoprostol, 2 days after you take Mifeprex (Day 3), to end your pregnancy. But, about 5-8 out of 100 women taking Mifeprex will need a surgical procedure to end the pregnancy or to stop too much bleeding. More information about this should come from your doctor.
As to where to get it, you might want to ask your doctor if she/he offers it--usually OB/GYNEs and family doctors. You can also check for a list of providers who can provide Mifeprex here:
National Abortion Federation (NAF)
For methotrexate, the instructions or dosage depends on the condition for which the patient is taking the drug. Methotrexate tablets or injections can be purchased from pharmacies as long as you have the prescription from your doctor.