We're very lucky around here. Have a small nursery just up the road and you just order your wallflowers and stocks and they pull them when you are ready to collect. Had some beauties! Must admit 'though, have always avoided those in my local garden centres - don't really trust them and also, they don't tend to advertise which varieties they are.
Sorry, Wahaj, down in Kent, not much use to you. There may be some nurseries near you. Local allotmenteers may know :)