You can use 3 single phase transformers and unless you have a scrap 3 phase transformer to obtain the core from that is likely to be your best bet.
Three phase transformers have 3 equal sized limbs and one phase is wound on each leg.
This works because the instantaneous sum of the 3 magnetic fields is zero.
You can use any combination of star and delta, but star/star is usually used with a neutral. If there is no neutral it is usual to have a delta winding to keep voltage balance.
Flux