Check out this pic--it's my kit with a cymbal boom stand in the left side. Look at the stand, it has a clamp-on accessory bar that I've added a separate boom stand to for another crash, so there are 2 crashes on one stand:
Gretsch Renown Maple Kit2 picture by dorussello11817 - Photobucket Pearl Gibraltar and
Tama all make em...
Buy Gibraltar Cymbal Long Boom Attachment Clamp | Clamps | Musician's Friend
A smaller cymbal arm and clamp, (cheaper):
Buy Gibraltar Cymbal Arm Mount | Cymbal Holders & Hardware | Musician's Friend
Here are some clamps that you could add a boom stand upper assembly to any other stand:
Buy Gibraltar SCBGC Grabber Multi Clamp | Clamps | Musician's Friend
Buy Gibraltar SC-4425G Standard Clamp | Clamps | Musician's Friend
Here is a bass-drum hoop-mounted stand:
Buy Gibraltar Bass Drum Mounted Cymbal Arm | Cymbal Holders & Hardware | Musician's Friend
There's tons of options, these are just the
Gibraltar offering.
DW even makes "Dog Bones" that clamp onto other stands....