Answer: Yes, Black MiQuri does restock about once or twice a year, but only a few of their most popular designs which are usually the Napoleon designs. Two examples I can recall are their LANCER jodhpur pants and the Napoleon parka which have both been released twice. They will also tweak some of their past clothes. This Napoleon dinner jacket is a longer version of this 4way Napoleon jacket without the chiffon part. Some of their products are actually old designs from the designer's previous brand BANANA FISH. Black MiQuri is still a fairly new brand, so don't expect too many re-releases.
If what you're looking for is sold out on their online shop, you can try having a shopping service check one of the physical KERA Shop locations. If it's not available there, then the only other option is to look on second-hand sites. If you're feeling a bit lucky, you can try tweeting @BlackMiquri. Designer 九朗-san checks very often and sometimes replies back in English, too. Do keep in mind that they do not currently ship overseas and they are not very popular internationally yet, so every request is not possible.
Feel free to ask me any questions over on my tumblr or message me via LJ!