For the walker I found this:

http://sketchup.google.com/3dwarehouse/ ... revstart=0

http://sketchup.google.com/3dwarehouse/ ... revstart=0

For the rower I'm not sure if you mean a gym machine like these ones:

http://sketchup.google.com/3dwarehouse/ ... revstart=0

http://sketchup.google.com/3dwarehouse/ ... revstart=0