I am not sure that Mountain Lion Catnip is still in business. You could do a Google search, and call or write them snail mail. IF they are still around, just buy some catnip and seperate the seeds. But like I said they may not be. Either they retired, died or otherwise arent doing it anymore. I have a very small amount of seed I separated from a tablespoon of Mtn Lion Black Tie, from about 5 years ago. I intend to keep that strain alive, but it will be a couple years of cropping just for seed, and testing to see if its really a better strain. According to the people at mtn lion, some of the other catnip places bought there stuff, and mixed it in to make commercial schwag a slightly higher quality.
Pet Stores sometimes have mid grade catnip. Buy the one that smells the best, and seperate the seeds. IF its good catnip bud, it has viable seed in the seed pods. IF they have the stuff in the plastic tube, whole bud, nice 3" coloa's.... that is the Mtn Lion KNOCKOFF... but I havent seen that for years.
There is one place in California selling catnip in green prescription bottles.. with names like "Kitty Skunk", Kitty Diesel, Kitty purple purp purping purplizing purplexinator, etc. Likely its novelty more than it is good kitty bud.... but if it smells good, it should be a good strain.