If you live in, or near a large city, I believe you may be able to find a health food store or grocery that can order it for you.
I get the 500g bags for about $13 from a discount HF Store where I live.
I get the berries and grind them myself OR the hawthorn berry powder.
I have never used the flowers/leaves, but may one of these days... I understand the whole plant is beneficial for BP among other cardiovascular related issues.