Uh, ya...
The mod on the Buy and sell was probably sold, because they are better and more popular mods.
And yes, Playthegames gets all types of mods, and they actualy had to write on the web site "You cannot request which kind you get" because they probably don't want to deal with all the people who start crying about it.
And about gettings mods, whats with your obsession with the internet?!? Most internet stores clear room for new consoles and whatnot. If you want to find things more likely you'l have to go looking for it at a real store, because its already so late in the game for Saturn. If you wanted to find stuff like that, your several years too late!!!
Its the same thing like the Sega Genesis for example. It was infact very popular, but im also equaly sure it would be very hard to find any store who sells them still online. Your best bet would be to go looking in retail stores in person for someone if you wanted them. But that dosn't mean for a long shot its hard to find, or unpopular.