front1wayfreak: Actually, just about EVERY major aftermarket company has a line of hopups for the R40. Not to mention the stuff from HPI.
3racing
Integy
Kawahara
HPI
all make hopups. Most of them just haven't made it to the market yet. Most are listed as "Coming Soon".
HPI Japan has a rear adjustable dual blade type sway bar for the rear on their site. Don't know when/if it will reach the states though.
http://www.hpiracing.co.jp/
Just type in R40 into the search bar, then start clicking links. You'll eventually run across the hop ups page.