I buy my parts including this impeller that I picked up 2 weeks ago for a rebuild I'm doing this winter at Oldport Marine in Newport, RI. They are an authorized Yanmar parts supplier. Call 401.847.9109 - Meredith Leblanc can get you this, and just about any other part for your Yanmar. She's good!
http://www.oldportmarine.com/

The part numbers are as follows:
Yanmar Water Pump Impeller 104211-42070
Yanmar Water Pump Gasket 104211-42090

Look on page 46 of this document and see if it is the same pump you have:
http://www.guillermo.ca/pdf/yanmar.pdf

Good Luck!
Bill




[This message has been edited by whk (edited 11-20-2006).]