I got them here:
They ship from China (surprise surprise), and took about 3 weeks for them to get to me. The price seems to fluctuate a little, depending on the listing. Maybe a dollar, one way or the other. They aren't the easiest to build on, they are pretty dinky. They are basically the same size as a BVC coil.
There are mixed reviews on them. I took a chance and really like them. I wasn't going to (or be able to) continue buying the BVC coils. So, the Mini would end up useless, for the most part, once my present stock of coils was gone (about 4 packs). So, for the price of a pack of coils, I gave the mini RBA a shot, and like it.
They do try your patience and building skills...lol, but I think it's worth it.