If your Geo Metro is a 92 to 94 year model, you can pull the instrument cluster out of a Suzuki Swift GT (same years) or a Geo Metro Convertibles (92 & 93) or later year Geo Trackers & Suzuki Sidekicks (96-98). Those instrument clusters are all interchangeable and had tachometers.
If you have a 95 and up Metro, I believe you can still try the above instrument clusters, and it might work.
For instance, something like this...
http://cgi.ebay.com/ebaymotors/ws/eB...tem=7965107799