Hey Michael
What I did was found these sites very useful in my gamertag hunt:
http://checkgamertag.com/ <-- Searches for any taken gamertag and can give alternatives if the one you are hunting for is taken!
(However, it cannot view v1 Gamertags)
[A 'v1 gamertag' is a gamertag with 5 silver stars, the original xbox logo for the picture and 0 Gamerscore]
Also, try this site out as well!
http://gamertagcreator.com/
What it does is generates user-suggested gamertags, along with computer generated suggestions. Highly helpful. However, around 33% of the user suggested content is either a troll or already taken.
Another thing, if you are searching for Original gamertags, be careful of scammers! Don't be afraid to also get something that's Semi-oG. They are easier to acquire and sometimes can be admired more!
Wish you luck with your hunt!