I go to the first aid kit hanging on the wall at work and help myself to 1 or 2 little such packets when I need refills.
But you don’t have to buy from a commercial / industrial supplier. As you observe, searching on Amazon for “triple antibiotic packets” finds numerous offerings of 144 such packets at 8 cents each to 25 packets at 22 cents each. Seems an ideal thing for someone to order up before the next GGG and assemble variety packs of them.
One such item I’ve never seen in single-serving packets is an antifungal ointment. OTOH, if you need it, you need it every day for a week or maybe the entire trip, so perhaps a small tube is best anyway.
Not for lotions, but for the pills like in some of those packets, you can order up an assortment of tiny Ziplock bags on Amazon (I got 500 for $9), label with a Sharpie and put 8-20 pills into each. Of course, then Amazon shows you other drug-dealing paraphernalia for weeks afterwards . . .
I love medical professional samples because 1) they’re tiny, 2) they’re labelled with the contents which is better than generic blank containers, 3) you can refill them from larger containers, and 4) contain prescription drugs that otherwise aren’t available in such small containers. Oh, and they’re free.
For refilling small tubes, mostly I squeeze them and let them re-expand with the opening submerged in a pool or capful of bulk lotion. For my fleet of two dozen tiny professional sample tubes of high-end sunscreen, I use a turkey marinade injector from the grocery store ($10) to fill up all of them at once, squirt any leftover back into the bulk container, and then wash it out well. 
If you’re looking for a container to serve as a FAK on a UL trip, use a dyneema ditty bag or a Ziplock, but for a day hike, Scout trip, or in the car, go to Walmart’s Back-to-School aisle in late August and buy red zippered pencils cases for $1 each. I buy a bunch in school colors for math competition supplies and write onto them in Sharpie. If there’s something you haven’t committed to memory (signs and symptoms of heat stroke versus heat exhaustion; stages of hypothermia; etc) xerox/laser print it (not ink jet) and use the Rite-in-the-Rain goo or just Thompson’s WaterSeal for your wooden deck to water proof the paper (which, when you think about it, is wood).