where you at? in ATL you can hit up garage sales and swap meets on the south side and find some classic shit.
in LA there are big swap meets and flea markets in long beach and pasadena, or you can check out craigslist and look for garage sales.
if there is a specific piece of vinyl you want in LA you can try amoeba music in hollywood. they have just about everything. you'll pay for it though. i paid $10 at amoeba for a single tower of power LP. meanwhile i hit up a garage sale in the suburbs and walked away with 4 crates full of stuff from the 80s going back to the 40s for $100. garage sales are where its at.
the other thing is, and this is just me running off at the mouth so pay no mind, that pretty much every mainstream soul and R&B record has been scanned hard by producers of all levels for samples. the temps, four tops, bobby womack, o'jays, all of that classic shit has been hit hard. go outside the box, look at old country and gospel music. shit like marty robbins or tennessee ernie ford. look for old school latin music, too. just my random thoughts.