I purchased new limbs but you can easily find doll parts on ebay
or at many thrift stores. You'll want fairly large ones and they should be vinyl and not porcelain. Wash them well in a dishwasher or by hand and use some heavy washers or bolts (that also should be washed) to weigh the open ends of the limbs down. Stainless steel would probably be the best material to avoid nasty chemicals in your brew.