A pre-fold is a nappy made from several layers of cotton muslin sewn into a square that you then fold into the shape of your choice and hold in place with a well-fitting wrap or a nappy nippa (or even a pin). I don't sell prefolds for several reasons.
One is that I don't rate them much - they don't contain poo as well as a nappy with elastic at the legs and top does and they're not as absorbent as a good old-fashioned terry square. When prefolds first appeared in the UK in the late 1970s, we thought they weren't a patch on a decent quality terry square and, without the elastication round the legs and waist that a fitted nappy has, the wrap used with a prefold often gets dirty and needs changing. This means you can end up having to buy a lot of wraps and so it all ends up being not as cheap an option as you thouight it would be.
Another thing I have against prefolds is that, once your baby too big for the prefold to be fastened round them with a nappy nippa, but just sits as a rectangle between the baby's legs, the wrap is in direct contact with the baby's skin. I can't believe that feels comfortable! A terry square or fitted nappy goes round your baby's sides as well as between the legs, so only soft absorbent cloth is in contact with the skin, not the PUL wrap.
The third reason I don't sell prefolds is that they are indestructable and last forever so, if you want some, get some second hand! That's the most environmental type of nappy you can buy - a preloved nappy. There are often perfectly good pre-folds on sale that have hardly been used - maybe because their owners didn't like them any better than I do. Try Gumtree, Preloved etc.
Having said all that, prefolds are cheap and very easy to wash and dry. They can be soaked in Napisan or biological detergent, dried on radiators and generally treated roughly. They work quite well on little babies who don't move about much and so make quite a good nappy for a newborn if you want to use cloth from birth, before moving on to a pocket, all-in-one or fitted nappy. (But I think I would still prefer to use a terry square fastened with a nappy nippa!)
I do sell wraps suitable for prefolds - either the Littlelamb or the Motherease Rikki are very suitable - see the Wraps section