un til early fall to plant outside and would the fall give the roots enough time to establish?
This article will help you in caring for these: https://www.gardeningknowhow.com/edible/herbs/arnica/how-to-grow-arnica-herbs.htm
Check you local garden centers.
Do a Google search for sellers. Try Ebay or Etsy; they are often good sources for plants.
A Sunny area but the leaves seem to get scorched from the very hot summer we are having. My question is should I plant it in full sun or partial?
Brown leaf tips or edges are usually due to too much or too little water. I would plant it in part sun, though, if you think it is getting too much sun.