For small growers, buying in bulk is pointless since surplus seed, onion sets and potatoes are likely to be wasted. But it’s usually possible to find smaller quantities in any good garden centre.
Better still, buy your veg online. I googled ‘onion sets’ and discovered that Dobies (www.dobies.co.uk) offer ‘Sturon’ onion sets in 200g packs – you surely wouldn’t want less than that! ‘Golden Gourmet’ shallots also come in 400g packs which would translate to about 15 individual shallots. Many other suppliers offer similar quantities.
Another alternative, particularly if you garden on an allotment, is to join forces with other growers and buy as a pair or in a group. That way, you can go for a wider range of varieties and then allocate these among yourselves. It is also a friendly and pleasant way to acquire seed.