We've got in an inventory of Grand Wing Servo S03N standard servos. These pack quite a bit of power, and prove to be pretty good for standard servo applications.
We're sorry to say that the RM1 is no-more. The RM1 is dead; long live the RM1. (I never understood that phrase...) All hail the RM1a!
The replacement for the RM1 is practically identical, except that there aren't any pre-attached motor leads, and there isn't an output gear. Fortunately, we've found that the output shaft is indeed 1.5mm, which matches our RW wheels nicely. Slide them together, use a dab of cyanoacrylate (soooper-glue!), and it's an ideal match for building Herbie-style robots.