I didn't see anything like this anywhere else on the site. This is a list of Shadow Pokemon in Colosseum. Not XD, because there are different pokemon. I'll try updating this list daily.
I'd love to see this as a guide once it's finished, but that's up to the mods.

???Will be completed ASAP!???

To avoid any confusions with Ho-oh, here's what to do:
1. Snag & Purify all 48 Shadow Pokemon.
2. Register your in-game team (not GBA team) into the Colosseum Mode.
3. Conquer the Colosseum Mode Mt. Battle VS 100 Challenge. Ho-oh will then be put in your PC in Story Mode.

Currently listed shadows: 37/48

Pokemon / Trainer Name / Location:
/ Miror B. Peon Trudly / Phenac City
/ Mystery Troop Rosso / Phenac City / Snagem Base* / Shadow Pkmn Lab*
/ Rider Nover
/ Rogue Cail / Pyrite Town
/ Cipher Peon Nore
/ Miror B. Peon Reath
/ Miror B. Peon Ferma
/ Hunter Doken
/ Rider Twan
/ Rider Sosh
/ Hunter Zalo
/ Cipher Admin Miror B. / Miror B.'s Hideout / Realgam Tower / Deep Colosseum*
/ Cipher Peon Skrub / Agate Village
/ Cipher Admin Dakim / Mt. Battle / Realgam Tower / Deep Colosseum*
/ Bandana Guy Divel
/ Rider Leba
/ Roller Boy Lon
/ Rider Vant
/ St. Performer Diogo / Pyrite Town
/ Cipher Peon Kloak
/ Cipher Admin Venus / The Under / Realgam Tower / Deep Colosseum*
/ Hunter Frena
/ Chaser Liaks
/ Bodybuilder Lonia
/ Rider Nelis
/ Cipher Peon Cole
/ Cipher Peon Lare
/ Cipher Peon Vana
/ Cipher Peon Lesar
/ Cipher Peon Tanie
/ Cipher Peon Remil
/ Cipher Admin Ein / Shadow Pkmn Lab / Realgam Tower / Deep Colosseum*
/ Cipher Peon Arton
/ Cipher Peon Baila
/ Cipher Peon Dioge
/ Cipher Peon Verde / Phenac City / Snagem Base* / Shadow Pkmn Lab*
/ Cipher Peon Bluno / Phenac City / Snagem Base* / Shadow Pkmn Lab*

*Available after Evice is defeated.

I think your missing Ho-oh unless I'm mistaken don't you get him at the end of battling those 100 trainers

do you get something when you get all shadow pokemon?

Answers both Qs.