J & G sales, or cheaper than dirt if all you're looking for is surplus fmj. If you're looking for the lake city long range, I would say either gunbroker.com or midwayusa.com. If you have the time and the patience to find the components, reload.
Academy had some over-run Winchester white box 147 grain FMJ for $12.00 a box the other day. 60 cents a round for .308 Ball is a pretty good price especially since there's no shipping costs.
If you reload, Widener's had some 145 grain FMJs for a real good price. I use 43 grains of IMR 4895 with that bullet for the 100 yard matches at Wichita Falls.