I know this has been done a million times (I have even started this sort of thread multiple times in the past!), but I can't apparently get enough of this sort of geek speculation!
Here are some available Rebel pilots that could still be used:
X-Wing Pilots from Rogue Squadron
Arhul Narra: I had never heard of this guy, but being listed as a co-founder of Rogue Squadron alongside Wedge and Luke makes him a very attractive "Ace".
Gavin Darklighter: guy from many novels
Flew Against a Death Star, Yavin or Endor (and died, like Biggs & Arvel)
Pretty select company. These people have screen time, too.
John D Brannon: X-Wing, Red 4
Elyhek Rue: X-Wing, Red 7
Bren Quersey: X-Wing, Red 8
Theron Nett: X-Wing, Red 10
Tiree: Y-Wing, Gold 2 (shot down by Vader)
Davish "Pops" Krail: Y-Wing, Gold 5 (shot down by Vader)
Grizz Frix: X-Wing
Ekelarc Yong: Y-Wing
Sila Kott: A-Wing; female pilot
Keir Santage: X-Wing, Red 7 (flew into 2nd Death Star with Lando, Wedge, Tycho, Horton, and Farrell)
Flew Against a Death Star (and Lived!)
Gemmer Sojan: A-Wing vs DSII and GR-75 Transport pilot at Hoth ("Bearing Lifter")