Nobby...
Here is the link:
www.rocknrollercart.com/ But a word of caution here, I would not put the PSR2000 on top of - or under - your speakers, which is the only way I can think of doing it all in one trip - unless the keyboard is in a solid body road case. The RockNRoller expands, but not enough to accomodate speakers and keyboard, all on the bed of it.
Maybe you should consider a Kaces bag on wheels for the keyboard and a smaller, lighter hand cart for speakers and other gear. It would mean two trips, but you could drag the kb safely on level ground, lifting only to get it in and out of your vehicle as well as up and down any steps.
Trying to miminize the moving hassle is a project I have yet to perfect. I can't help but remember my father advising me to learn the harmonica.
Eddie