In truth every boat should be measured for a new sail, esp 30-40 yr old boats are likely to have been somewhat modified. The presence of the furler will automatically reduce the luff dimension for the sail as the furler drum and swivel shorten the overall length of the sail along the forestay.
If you're after a used sail, then you need to find a boat with similar (or slightly smaller - but not larger) rig dimensions. For a genoa/headsail the important measurements are the 'I' (deck to top of forestay) and the 'J' (mast to forestay on deck)
Since you have a furler you'd be best to remove the sail, stretch it out and measure it yourself, then surf the used sail sites with those dimensions in hand. Finding a decent sail a few inches short would be fine and the difference virtually unnoticeable - except that replacing a blown sail with a better one will make a difference, of course.
Another option is to choose a good sail that is slightly too big and have a sailmaker cut it down to suit.
There used to be a marine consignment/recycle outfit in Sidney.. not sure if they are still around; the only local one I can find is 'Bitter End' in Gibsons.
Still, I think there are Hood and Leitch & McBride lofts in the Victoria area. And of course the ubiquitous Craigslists, Ebay etc. Bacon's in the US will ship anywhere too, so browsing their listings may be worthwhile.
There are also significant savings in going to offshore/on-line lofts too, however you will lose the 'local service' aspect if things don't fit too well. Unlike Catalina, Hunter etc the Spencer is not so well known globally.