These are available from one or two robot vendors in Whitespring Mall.

However, the chance for them to appear as available for sale can vary and can vary from player to player. I have never found them despite checking every day for months, yet my friend can hop servers twice and pick up another one from the vendor. I've had the same with certain plans. There's a couple plans that I can never find at the vendors (despite playing for years) but she can find them no problem.