More specofically, from private stores in towns. There are a few private stores in Gludio and Gludin that sell D grade SS. More so in Dion. At least that's the way it is on Seigehardt. it's probably similar on other servers.
On some other server, it's the reverse: SSD for soul shots, SpSD for spiritshots and BSpSD or BSSD for blessed.
I usually see it where Soulshots are prefixed by grade but the Spiritshots are postfixed. So:
SSS = Soulshot S grade
*** = Soulshot A grade
BSS = Soulshot B grade
CSS = Soulshot C grade
DSS = Soulshot D grade
NGSS = Soulshot No Grade
and
BSPSS = Blessed Spiritshot S grade
BSPSA = Blessed Spiritshot A grade
BSPSB = Blessed Spiritshot B grade
BSPSC = Blessed Spiritshot C grade
BSPSD = Blessed Spiritshot D grade
BSPSNG = Blessed Spiritshot No grade
...No one really sells regular SpiritShots, so you won't see those unless you shout until you find someone who has the recipe and is willing to make some to order. If someone did make them I think they'd show up like so:
SPSS = Spiritshot S grade
SPSA = Spiritshot A grade
SPSB = Spiritshot B grade
SPSC = Spiritshot C grade
SPSD = Spiritshot D grade
SPSNG = Spiritshot No grade
...No one really sells regular SpiritShots, so you won't see those unless you shout until you find someone who has the recipe and is willing to make some to order
Unless you're playing on Franz and then you will see a few people selling regular sps.