Many years ago I watched a movie starring Sean Michaels, Buck Adams, Madison Stone, Holly Ryder, Alexandria Quinn and others.
I remember only two scenes: in the first scene Madison and Holly Ryder are doing lesbian sex when Sean Michaels arrives in their bedroom. Holly is scared because, as she says to Madison, she never fucked a black man. Madison tells her to be quiet and teaches her how to fuck a black cock, then starts a very exciting threesome scene.
In the second scene Buck Adams is on a sofa together with Alexandria Quinn: he tells her she must learn to suck cocks
to win a contest, I guess (I don't remember this scene very well). Then she starts to suck his cock and later Buck fucks Alexandria on the sofa.
Somebody knows the title of this movie? Thanks

Are you sure you have all the names right? According to iafd.com, all the names you mentioned have never appeared in the same movie together.

Maybe?

Shameless (1991, Sin City)
Scene 1. Brigitte Aime, Nina Hartley, Woody Long
Scene 2. Nina Hartley, TT Boy
Scene 3. Alicyn Sterling, Buck Adams
Scene 4. Madison, Sean Michaels
Scene 5. Debi Diamond, TT Boy
Scene 6. Carolyn Monroe, Cole Stevens
Scene 7. Alexandra Quinn, Marc Wallice
Scene 22. Frankie Leigh, Jon Dough

Deep Cheeks (1991, Rosebud))
Scene 1. Alexandra Quinn, Madison, Sean Michaels
Scene 2. Buck Adams, Marc Wallice, Samantha York
Scene 3. Melanie Moore, TT Boy
Scene 4. Brigitte Aime, Saki St. Jermaine, Tom Byron
Scene 5. Brigitte Aime, Debi Diamond, Sean Michaels, Tom Byron

Anal Climax 1 (1991, Rosebud))
Scene 1. Madison, Melanie Moore, Sean Michaels
Scene 2. Alexandra Quinn, Buck Adams
Scene 3. Kym Wilde, P.J. Sparxx, Tom Byron
Scene 4. Carolyn Monroe, Saki St. Jermaine, TT Boy

Good luck finding any of these...

its very likely you will not find this

Alexandra Quinn was under age at the time and all her titles were pulled.

I forgot ...gracias, Mike.

Thank you so much, guys.