Grouse,
I like to start out with a small pack that usually comes with a sabot (e.g XTP's, Barnes, Shockwave, SST), just to try them. I have a good inventory of Harvester and MMP sabots now, so I can experiment, looking for the loading pressure I want. I have a pretty good idea who makes some of the supplied sabots (Barnes are MMP's), but again the sabots may be old stock (or old formulation).. so why take a chance. Better to buy the sabots direct and be sure of what you got
Once I find that "magic combo".... I'd rather buy only the bullets, in bulk. Like you said, not many are offered like that.
Right now I have bulk bullets in 300gr XTP, 200gr 10mm XTP, 250gr Speer Gold Dots, and 260 Speer JHP. Hey those are all pistol bullets... that's probably the only reason they are available in bulk.