If you don't find anything nearer to Kalyves, I can recommend http://olympicbike.com
Markos, the owner, is a good guy, bikes are in great order and their service is reliable. We've used them a couple of times.
For rentals outside of Rethymno, they charge EUR 25 delivery per bike. Expensive for just a couple of days, but more tolerable if you are renting for maybe a fortnight and you can't find an alternative. Olympic are open now and throughout May.