Jaxtr does not sell shares in any stock exchange in the world, and that name is not listed in the database at Companies House (i.e. it's at least not a UK based company). Looking at their website, they are based in California somewhere (if that's the state called "CA" in addresses!). They were formed in 2005, so are not very likely to have floated (or IPO'd) - especially as that is not a news item on their "Press release" area.
If you wish to invest, you would have to contact them direct, although I suspect the levels of investment required to get their interest would be such that most folk could not afford to do it.
