I just compound it myself. Carnitine base, Bac water, .22 wheel filter, vials, caps, crimper.
If you want to be super anal about sterility make a still air box out of a 60 gallon Sterilite tub. Ive got easy access to sterile environments to compound with flow hoods and such though.
It's upcharge is ridiculous from anywhere you buy it. I can put a vial together for about 2 dollars vs 40+ from vendors.
Carnitine itself is incredibly bactereostatic and fungistatic at concentrations above 15mg/ml. Getting contaminated would be pretty incredible at 400mg+/ml.
You can also compound single doses on the fly if you don't have vialing materials, but that's a huge waste of filters tbh.