Who are you looking for specifically? I hadn't been thinking of selling mine yet but I have completely lapsed on collecting them so I'm not too attached (Except to Galactus. Big G isn't going anywhere, ever!). I started around Wave 2 (Plus Cap from Wave 1) and bought pretty religiously for a few years. I have many of the build a figures complete. Off the top of my head I have complete Galactus, Apocalypse, Sentinel, Giant Man, MODOK, Brood Queen, and Fin Fang Foom. I have pieces of Blob and Onslaught. I think I finished Annihilus but not 100% sure. I have some of the box sets like one of the FF ones, and a Spider-Man one that was not Sinister Six. But being unable to find more than 1-2 per wave and the price getting jacked up to all hell per figure drove me away. I haven't bought one outside of clearance in years now. For a while I switched to the 3 3/4" figures, then those started spiraling out of control too. I gave up.
Now the majority of them live in a couple of rubbermaid tubs in my basement, with some still being in glass cases because I've been too lazy to take them off the wall.
Mine are all loose except stuff I found on clearance in recent years or stuff I considered too ugly to display (Looking at you Diamond Emma!)