I make my own by mixing equal parts of beeswax, olive oil and some other stuff, sometimes. The beeswax/olive oil alone works well enough, though. I just have a cake of hardened lube which I rub into the grease grooves on the minie when I'm loading.I think any vegetable oil or animal fat will make a servicable lube if it can be given the proper consistency, which is what the beeswax does. Regular canning paraffin wax you can buy at any grocery store can be melted with the oil to make the right consistency, too.
I've not personally tried the commercial black powder lubes. Two I know of are SPG and Bore Butter.
Steve