I make my own, using suet, oats and whatever seeds I have handy.
I take an old yogurt pot or plastic cup, and make a small in the centre of the base to pass through a length of string. To the end that will be at the top opening of the cup/pot, I attach a small stick, slightly longer than the diameter of the pot. This will act as both a retainer for the fat ball to stop it sliding off and provide two pegs for a small bird to stand on.
Make the mixture in a pot until it’s the right consistency and then spoon it into the plastic container right up to the top. I find it useful to put a bit of tape over the hole where the string comes out, to lessen any seepage. The string does get in the way a bit but it still works.
Then they sit upright in my freezing porch until set, at which point I can slide the pots off the fat balls and hang them in the garden.