Solid birch lumber for furniture production

Looking to source solid birch lumber for indoor furniture frame production.
Specification:
Dimensions: 21×45×3000 mm
Finish: S4S preferred, S2S2E acceptable
Drying: Kiln-dried, heat treated
Defects such as knots and false cores are acceptable if they do not affect durability
We are looking for a long-term partner and may increase volume depending on quality and service.