DS was on adeks drops as a baby. But we had issues getting them from time to time. I do recall using poly-vi-sol for a few weeks until we could order some from the CF Services pharmacy, but we were warned by the dietician not to do it long term as the adeks had zinc in them and the others didn't. We also supplemented a drop of A & E when he was a baby as per his doctors instructions, as well as a vitamin k tablet once a week.
When adeks drops were eliminated and aquaadeks started, we did okay until those too were on backorder. Fortunately, we'd gotten a sample of chewable ABDEKs from Sourcecf for free from the clinic and we substituted those. We now use those exclusively.
I think the key is just making sure your child is on a cf vitamin. Our insurance doesn't cover vitamins, so I find the cheapest price and order three bottles at a time so I can get free shipping.
Oh and sometimes, because DS was the only baby at our local CF clinic, we'd get free bottles of adeks from time to time. Wouldn't hurt to ask...