Well... there is a Gisborne Road Cycling Club
http://www.gisbornecycling.co.nz/
They do have a link to their calendar of rides, so hopefully one/a few of those fit with your holiday plans
You just missed Gwaloop which they ran (I think the first time this year) a few weeks back
http://www.gwaloop.co.nz/
I have only been to Gisborne once, and that was to support my lads doing the interclub competition between them and our club, Ramblers (2 rides up there, 2 rides down here) earlier this year
In 2008 I'm getting a bike racing licence and then I'll do the interclub with Gisborner too!
Don't know if you have been there before, NMT, but I was very taken with it... the beach is stunning. We stayed in the holiday park on the waterfront - very very nice. My youngest son couldn't sleep very well and was up very early on th Sunday we were there, and we went walking in the morning twilight - just beautiful.