I thought it would be a good idea to start a thread for the locations of the bail bonds missions so here are the first 2. Hopefully others can add some more to get a good guide going
#1 Ralph Ostrowski
Davis Quartz Quarry
#2 Larry Tupper
Grand Senora Desert
#3 Glenn Scoville
On top of Mount Chiliad (just southeast of the cable car station)
#4 Curtis Weaver (Thanks to Nozza x360a for this one)
He is located at the North-east point of the map. From Paleto Bay (the town on the North-west coast), head East along the main road. Keep going until the map shows a road that has a little loop in it.
Just a little down from that, is a hidden trailer park. If you zoom in on the map, you can see the grey road coming off the main carriage way. It looks like a snakes tongue.
Here's an image to help.