The ONLY place bell reliably provides this info is at the top of your bill where they announce promotions and previews. Channel 230 occasionally lists lineup changes and channel previews but hasn't listed anything lately.
My only other suggestion besides checking back on this site for general channel launch announcements that usually always show up here eventually is to just check your EPG and look for channels with (INFO) in the programming description.
There is NO one website from Bell that specifically lists free preview channels like what you're looking for unfortunately.
I may be wrong about this but I just noticed this morning that Action is a "free preview until Oct 31st?" I've had it in my custom list forever so anyone know what's going on? Is this something like the Scream switch to Dusk (which annoys the hell outta me).