***Wanted*** WP-DC30 Housing for Canon A75.
I’d like to buy one. Anyone know where to get one? Used or new?

Did you do any looking online for one of these ?

http://www.amazon.com/Canon-Waterproof-Case-WP-DC30-Powershot/dp/B0001GMSZI?tag2=gp04-20

they are at amazon.com

This place in the UK
http://www.camerasunderwater.co.uk/d_stills/canon/wpdc30.html

this place in Canada
http://www.vistek.ca/details/details.aspx?WebCode=215485&CategoryID=UnderwaterCases

This place in Australia
http://www.digitalcameras.com.au/product.asp?productid=2473

Hopefully that helps.
If you want a more local shop dealer then let us know where you live and I am sure we can find you one of those as well.