Hi Dan,
If it's the lens I'm thinking of, it was indeed well respected glass in it's day, where Sigma lens were pretty mediocre at that time (oh how things change!)....also made when Vivitar was much more than the mere brand printed onto cheap entry level digi' cameras as it is today.
RE the lens mount adapter. loads are available for the Canon EF (EOS) mount. The fact that the Canon bodies lens large mount throat diameter makes life easier.
Here in the UK, SRB filters are generally the best people to go to, to get lens adapters of all sorts.
However, there are plenty around on the dreaded ebay. I bought one from a company called Roxsen, who also trade on ebay. I have no personal connection with the company, but know I've had good service from them in the past.
A quick search on ebay reveals quite a few.
here's one as an example;
http://cgi.ebay.co.uk/Contax-C-Y-len...QQcmdZViewItem
Worth a mention is the the focus confirmation feature that some adapters have. To be honest if I were to buy one again to put my Contax fit lenses on Jacky's (wisher) Canon digi camera, I would've probably gone for one with the AF confirmation....unfortunately Jacky's camera doesn't benefit from micro prism, fresnel or split prism focus aids on the screen, so the AF confirm feature might have been a nice thing to have.
Here's an example of a mount adapter with AF confirmation;
http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=008
Now for the brutal honesty!
We've only actually used the adapter a few times...Jacky's used it once or twice, but the majority of my lenses are too big and heavy for her, and she likes auto focus!
Hope this helps.
cheers
Joe