Not sure about the situation now, but back 20 or 30 years ago you could have gotten all the large parasitic specimens you wanted by going on a salmon charter in Lake Ontario. We would often catch salmon with one of those big suckers...literally!...hanging off the side.
They usually let go as soon as the fish was netted and lifted out of the water, but occasionally one would make it into the boat. They never ever made it back out...
I'm not squeamish or frightened about handling creepy-crawlies...venomous snakes, arachnids, etc...but I simply couldn't stand touching lampreys. When Jeremy Wade did it in an episode of River Monsters he had my total respect.