I live in Chiang Mai and need to send a regukar size motorbike back here from Chiang Rai. I should be very grateful if my fellow visa.com members in Chiang Rai could avise as to a company offering this service.

On lamposts all over Thailand, there are adverts from pick-up owners who move stuff for a fee. If you cannot speak Thai, I imagine you will need a Thai speaker to assist you in making the arrangements.

 

Check out your nearest lamposts.

post office

Maybe ask around at the bus depot?

The inter-city Song Thau (often called "mini-bus") would be happy to do it.  Look for a blue songthau at the old city bus station.

Post Office use to be 2000thb for regular size (up to 200cc I think) mc anywhere in Thailand.  Add 1000thb for larger bike.

Many thanks for the helpful suggestions - much appreciated.