Reply to Samples for transitions..where At?

Hey guys

Im wondering, where can i get samples for transitions...

For example, im mixing on the last 32 beats of a song, with the 32 of a new song, when the old song is about the end, i wanna throw in a sample, like the ones you hear in edm songs before a breakdown, or before a drop...those heavy snares that sound like SSSSHHHHHTAAAA, you know?

I know most artists add some of this on the last beat of the song, but many dont.