Oh that's easy, there base was a old underground bunker that the Combine had also used to store captured but unrepaired Clan Mechs, also stored in mothballed Overlord Dropships that only needed to be refueled and resupplied and were kept in underground launch pads. Now while Galedon's surface was persona non grata the Black Thorns could an did scrounge up the needed resources to launch there dropship fleet. They rendezvoused with a Jumpship in orbit willing to take on passengers from Galedon ignoring the signs saying "AVOID! DEATH HERE" and took the Black Thorns to Galatea were they lived happily ever after. :D