If it is available, where is it available?
What do you mean by "SoC"?
Actually, the SoC is just the CPU/GPU. The memory is a separate item, not purchased at the same time as the SoC - so you can order whatever size you want. (i.e. 128,256, or 512). But, and its a big but, its unlikely you would be able to purchase either the SoC or the memory in small (i.e. <10k) quantities.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Please direct all questions to the forum, I do not do support via PM.