I fairly sure that RDX crystals arn't available commercially, especially in crystal form as they
are too unstable. They would be combined with a plasticizing agent for greater stability.
These would be things like C4 and most plastic explosives, good luck trying to buy those!

Unless anyone else knows where to buy them, then I'm waiting to be corrected

As for wether or not Hexonit is more powerful than RDX, i think Hexonit was first developed
by the Russians for use in underwater mines and depth charges.
This is because of its ability to stay submerged in water for long periods of time and still
detonate.

Not quite sure of that fact, Ghost?

I don't think there is a huge amount of power difference between the two, it just
depends on what you want to use it for.

raw RDX is rarely used as an explosive filler, is's all about the binders and plastiques these days to get the required vod and physical properties for the task at hand... you won't be able to buy it.

edit: Hexonite, re: underwater stability... yeah, that sounds about right.