Last year I bought a healthy Salix Kilmarnock during the last summer rust coloured powder appeared on the leaves

Green thumb time on the willow. Scratch a bit of bark with your thumb nail and if there is green under the outer layer of bark then the plant is alive.
Camellias generally like an acid soil and shelter from early morning sun on frosted leaves.

the catkins are male flowers and many willows are either all male or all female plants. Did yours have catkins when you bought it? If not it might be female in which case the flowers are very small and insignificant. If you stripped it of its leaves then it may not have been able to make flower buds for this year.
As Owdboggie says scratch the bark with your nail.
Camellias prefer acidic soils and dont like east facing windy sites.

I believe that the lack of early life could be that you removed all of the leaves in summer rather than just a few but the rust could have killed the plant especially if it was immature. As suggested try the thumbnail test. Remember the plants that you have seen in the garden centres would have come from abroad and been raised under glass to bring them along early so will have been more advanced than one that has been raised in the garden.