My favorite 3He source would be "Planet X", if it exists and is an Earth (or perhaps even Mars) size planet out far enough that the temperature at the exobase is low enough to retain 3He in its atmosphere. Sure, getting there would be difficult, but this scenario assumes we have D3He fusion, which we can handwave would get the miners out there in a reasonable amount of time.

If it takes long enough to get there and back, folks back home might perfect p-B fusion in the meantime.

I don't think p-11B fusion will be possible. The groups attempting it look really sketchy (as in, talking about doing things that clearly don't work.)

It will take fundamental advances to get to p-11B fusion. A startup working today is anyway in no position to achieve such fundamental advances; that is more in the line of national laboratories, or would be if they were not fooling with ITER instead. Maybe some of the ITER work will be useful for other things.

For D-3He fusion to be useful, we have to hope that it will be economically viable to synthesize 3He, in the meantime. Arguably, we ought to be making and stockpiling tritium now so there will be enough 3He when we need it; but that might be too optimistic.