Aer Arann - ATR42 (48 Seats)
Aer Arann - ATR72-201 (68 Seats)
Aer Arann - ATR72-500 (72 Seats)
BA CityFlyer - Embraer 170 (76 Seats)
BA CityFlyer - Embraer 190 (98 Seats)
bmi Regional - Embraer 135 (37 Seats)
bmi Regional - Embraer 145 (49 Seats)
Cello Aviation - BAe 146-200 (50 Seats)
CityJet - BAe RJ85 (95 Seats)
Eastern Airways - Jetstream 41 (29 Seats)
Eastern Airways - Embraer 135 (37 Seats)
Eastern Airways - Embraer 145 (50 Seats)
Eastern Airways - Saab 2000 (50 Seats)
Flybe - Dash8-Q400 (78 Seats)
Flybe - Embraer 175 (88 Seats)
Flybe - Embraer 195 (118 Seats)
Jet2.com - B737-300 (148 Seats)
Jet2.com - B737-800 (189 Seats)
Jet2.com - B757-200 (229/232 Seats)
Monarch Airlines - Airbus A320 (174 Seats)
Monarch Airlines - Airbus A321 (214 Seats)
Suckling Airways - Dornier 328 (31/32 Seats)
Suckling Airways - Saab 340 (34 Seats)
Titan Airways - BAe146-200 (77/80 Seats)
Titan Airways - B737-300 (44/130)
Titan Airways - B757-200 (80/148/202)
I hope this helps however a broker may be able to suggest an airline/aircraft to best suit your needs using their own contacts. Of course you can cut out the middle man and contact the airlines directly.
What does have to take into consideration is the costs for positioning flights and it may be cheaper to use an alternative airport near Gloucester that deals with some of these airlines regular.
Cardiff, Bristol or Birmingham could be an alternative option for departure airports.