Try:
AlgarSerra - http://www.algarserra.com/
Transol - reservas@transol.pt
If you are heading to the Eastern Algarve also try Lepebus just over the Guadiana in Spain.
email: comercial@lepebus.com
I have used them in the past and I found them to be efficient and, at the time cost effective. They are often up and down to Faro Airport.
