Encoders:
www.usdigital.com
www.grayhill.com
Gyros and accelerometers:
www.analog.com
The Grayhill and Analog Devices products are available from DigiKey.com (among others).
I have used the Grayhill 61K, 61R, 63K, and 64R encoders in the past.
I have also used the Analog Devices ADXRS150 150 deg/sec gyro evaluation board (PDF:
http://www.analog.com/UploadedFiles/...XRS150EB_0.pdf)
The Analog Devices ADXL204 Evaluation Board is the same chip used in the kit accelerometer (PDF:
http://www.analog.com/UploadedFiles/...DXL204EB_0.pdf)
Good luck!