I used dried juniper from organic store bulk section. I would love to go and collect wild juniper which is supposed to grow in the mountains nearby, but that would be a task-and-a-half just to locate a bush. Plus I think most wild edibles are only around for a few weeks in the summer around here so I would need to time it well. I really want to do a proper sahti one of these summers by collecting juniper branches from Rockies and harvesting yeast from berries. It would be epic.
I made a mead a couple years ago and bottled a half of them with a few juniper berries and it did show a hint of juniper which was nice. Maybe bottle aging with juniper could work, though I would probably do a half and half again to see if I could pick up a difference.