hye..i just wanna ask for advice or suggestion. on how to start a group of divers tht can go on locating treasures or anything valuable.. all i wanna know is how.how to start..tq. 
Knowing the treasure that you are looking for would be a good start.
Do research on it & find out more about the shipping route ... all base on history.
Keep an open mind, listen to fisherman story, talk to locals & start finding out the location from them.
You can ask the fisherman for GPS reading or go with them & do couple of dives at the said location.
For sure you would need few divers, community like this might be able to help you as I m sure some of us are into treasure hunting.
Basic scuba equipment ...Handheld GPS... good diving buddies....hand tools ......having search technique underwater would be handy, IMO this is what you need for a start, until u can confirm the things that you are looking for, then start another planning.
;D