The SF722 last approximately 3 months if you have 6 capsules per day. I take 2 capsules per meal. You might want to start out at 4 capsule per day at first.
Do a google shopping search for “SF722 thorne” and this will show you all of the places that ship it in the UK and sort by price.
Buckwheat is available in a few forms. First buckwheat flour can be used for baking. Second the cream of buckwheat is similar to oatmeal and can be eaten for breakfast. Third, raw buckwheat can be cooked/steamed and is similar to rice/quinoa; you can likely find it in the bulk isle of your local health food or organic food store.