What you do is:
1. Buy Selenium on a world that it is traded, such as WG.
2. Transport the Selenium via spacecraft to a world where it is not traded, such as KB.
3. Sell Selenium into market or to your corporations.
4. Profit.
I do not have a presence on KB so I cannot resolve that shortage for you. I sell Selenium from time to time on FB market. I'd do it more frequently but I often find myself busy managing other things. I will probably increase my Selenium transports as time goes on because it momentarily makes me feel like a nice guy to resolve a world market shortage. As I said however, I cannot help KB until I establish a presence there, which I have not yet decided to commit to. I will probably eventually get around to plopping a presence down there someday, and then your Selenium shortages will sometimes be resolved.
It really makes no sense to me, though. Isn't glass made from sand (aka Silicon)? Is Selenium a mistranslation? Is there no sand on some worlds? It is what it is, so whatever. . .