Usually you have to transfer into being a PICC nurse from inside of a hospital, and then you can branch out outside of the hospital. Some community colleges and some private companies offer PICC training, BARD offers online training, but you have to still pick up the hands on. 99.9% of the training is actually hands-on training and trouble shooting. We say at our hospital it takes a good 6 months of being a full-time vascular access nurses to simply be competent, 1 year to actually be sufficient.
Personally I started out being an IV/infusion nurse at nursing homes, was hired into the outpatient infusion center at my local hospital, and then was trained to be a vascular access nurse.