Valerian is one that blooms like mad in June. White tall flower spikes and very fragrant.

Lilac bushes bloom in june, kousa dogwoods bloom white and pink. Some rhodies in june, and in early june many fruit trees.

The yellow perennials bloom mostly in late summer, sorry to say. You might be able to buy dahlias in pots that are already in bloom, and those come in yellows.

All the best.

Jim

There are some early yellow daylilies that bloom in June along with some coral bells.
Teresa