Yeah, don’t you hate when that happens? Interestingly, if you search for pig’s blood on Google, it directs you to another link to "Find pig’s blood at eBay", but, disappointingly and a little misleadingly, there are currently no auctions for pig’s blood at eBay.
Face it, this is not the sort of thing you’re going to find anywhere but at a slaughterhouse, a specialty butcher’s, or an old-fashioned farm. It’s not like there’s less supply these days, but the slaughtering and purging takes place at a lot fewer places. We’d pick up the phone and start with butchers - a motivated butcher might be able to get some from a slaughterhouse for a good customer, even if he never handles the stuff himself - and then move on to farms.