The big players selling to the consumer market (such as Qualcomm) really aren't interested unless you want to buy in 10k or even 100k / 1M quantities and they rarely (if ever) sell via the type of distribution such as digikey / mouser and so forth.
They are more likely to be with Avnet and it's subsidiaries, Arrow or another of the big distribution partners but they won't engage with small companies either (not worth the time and effort from their perspective). They also sell direct to their premium partners (who are buying massive quantities of parts usually measured in millions).
I have run into that with GPS chipsets a few years ago; we were selling perhaps 100 units per month but this particular supplier was not interested in less than 10k parts per month (not worth their time and effort basically).
What you really need to do is to identify what you want / need your SBC to be capable of and then choose parts that are available based on those criteria.