Don't know about cinefoil... but 'mulsin' can be bought at home improvement stores such as Home Depot for 'very cheap'. It is usually 'unbleached' so it has a 'warm' cast.
Upholstery supply houses would have 'bleached' muslin. such a store may also have other types of cloth to allow for lighter 'transmissive' moderation of the light, rather than 'bounce'.
You can also get white bedsheets at Target or Walmart...
Just one word of warning... these materials are not treated for fire, and so, need to be well away from 'hot' lamps.